diff --git a/ci/licenses_golden/licenses_flutter b/ci/licenses_golden/licenses_flutter
index 5c9e0ac454d9c..c05267758d76d 100644
--- a/ci/licenses_golden/licenses_flutter
+++ b/ci/licenses_golden/licenses_flutter
@@ -592,6 +592,8 @@ FILE: ../../../flutter/shell/common/shell_io_manager.cc
 FILE: ../../../flutter/shell/common/shell_io_manager.h
 FILE: ../../../flutter/shell/common/shell_test.cc
 FILE: ../../../flutter/shell/common/shell_test.h
+FILE: ../../../flutter/shell/common/shell_test_external_view_embedder.cc
+FILE: ../../../flutter/shell/common/shell_test_external_view_embedder.h
 FILE: ../../../flutter/shell/common/shell_test_platform_view.cc
 FILE: ../../../flutter/shell/common/shell_test_platform_view.h
 FILE: ../../../flutter/shell/common/shell_test_platform_view_gl.cc
diff --git a/flow/embedded_views.h b/flow/embedded_views.h
index b80f7b4ba5d54..14dd00cf5e8c8 100644
--- a/flow/embedded_views.h
+++ b/flow/embedded_views.h
@@ -253,6 +253,18 @@ class ExternalViewEmbedder {
   // This is called after submitting the embedder frame and the surface frame.
   virtual void FinishFrame();
 
+  // This should only be called after |SubmitFrame|.
+  // This method provides the embedder a way to do additional tasks after
+  // |SubmitFrame|. After invoking this method, the current task on the
+  // TaskRunner should end immediately.
+  //
+  // For example on the iOS embedder, threads are merged in this call.
+  // A new frame on the platform thread starts immediately. If the GPU thread
+  // still has some task running, there could be two frames being rendered
+  // concurrently, which causes undefined behaviors.
+  virtual void EndFrame(
+      fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {}
+
   FML_DISALLOW_COPY_AND_ASSIGN(ExternalViewEmbedder);
 
 };  // ExternalViewEmbedder
diff --git a/shell/common/BUILD.gn b/shell/common/BUILD.gn
index 66684679c3de3..3fab3317b094b 100644
--- a/shell/common/BUILD.gn
+++ b/shell/common/BUILD.gn
@@ -191,6 +191,8 @@ if (enable_unittests) {
       "pipeline_unittests.cc",
       "shell_test.cc",
       "shell_test.h",
+      "shell_test_external_view_embedder.cc",
+      "shell_test_external_view_embedder.h",
       "shell_test_platform_view.cc",
       "shell_test_platform_view.h",
       "shell_unittests.cc",
diff --git a/shell/common/animator_unittests.cc b/shell/common/animator_unittests.cc
index ed54ea5272be2..bf2ac9f5a9cf1 100644
--- a/shell/common/animator_unittests.cc
+++ b/shell/common/animator_unittests.cc
@@ -55,7 +55,7 @@ TEST_F(ShellTest, VSyncTargetTime) {
           return ShellTestPlatformView::Create(
               shell, shell.GetTaskRunners(), vsync_clock,
               std::move(create_vsync_waiter),
-              ShellTestPlatformView::BackendType::kDefaultBackend);
+              ShellTestPlatformView::BackendType::kDefaultBackend, nullptr);
         },
         [](Shell& shell) {
           return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners());
diff --git a/shell/common/rasterizer.cc b/shell/common/rasterizer.cc
index bce1b2bf036cb..ce456925c69ac 100644
--- a/shell/common/rasterizer.cc
+++ b/shell/common/rasterizer.cc
@@ -136,6 +136,16 @@ void Rasterizer::Draw(fml::RefPtr<Pipeline<flutter::LayerTree>> pipeline) {
     consume_result = PipelineConsumeResult::MoreAvailable;
   }
 
+  // Merging the thread as we know the next `Draw` should be run on the platform
+  // thread.
+  if (raster_status == RasterStatus::kResubmit) {
+    auto* external_view_embedder = surface_->GetExternalViewEmbedder();
+    // We know only the `external_view_embedder` can
+    // causes|RasterStatus::kResubmit|. Check to make sure.
+    FML_DCHECK(external_view_embedder != nullptr);
+    external_view_embedder->EndFrame(raster_thread_merger_);
+  }
+
   // Consume as many pipeline items as possible. But yield the event loop
   // between successive tries.
   switch (consume_result) {
diff --git a/shell/common/shell_test.cc b/shell/common/shell_test.cc
index 378375c5eac1e..cf7f9ed8d801b 100644
--- a/shell/common/shell_test.cc
+++ b/shell/common/shell_test.cc
@@ -260,9 +260,12 @@ std::unique_ptr<Shell> ShellTest::CreateShell(Settings settings,
                      simulate_vsync);
 }
 
-std::unique_ptr<Shell> ShellTest::CreateShell(Settings settings,
-                                              TaskRunners task_runners,
-                                              bool simulate_vsync) {
+std::unique_ptr<Shell> ShellTest::CreateShell(
+    Settings settings,
+    TaskRunners task_runners,
+    bool simulate_vsync,
+    std::shared_ptr<ShellTestExternalViewEmbedder>
+        shell_test_external_view_embedder) {
   const auto vsync_clock = std::make_shared<ShellTestVsyncClock>();
   CreateVsyncWaiter create_vsync_waiter = [&]() {
     if (simulate_vsync) {
@@ -275,17 +278,18 @@ std::unique_ptr<Shell> ShellTest::CreateShell(Settings settings,
   };
   return Shell::Create(
       task_runners, settings,
-      [vsync_clock, &create_vsync_waiter](Shell& shell) {
+      [vsync_clock, &create_vsync_waiter,
+       shell_test_external_view_embedder](Shell& shell) {
         return ShellTestPlatformView::Create(
             shell, shell.GetTaskRunners(), vsync_clock,
             std::move(create_vsync_waiter),
-            ShellTestPlatformView::BackendType::kDefaultBackend);
+            ShellTestPlatformView::BackendType::kDefaultBackend,
+            shell_test_external_view_embedder);
       },
       [](Shell& shell) {
         return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners());
       });
 }
-
 void ShellTest::DestroyShell(std::unique_ptr<Shell> shell) {
   DestroyShell(std::move(shell), GetTaskRunnersForFixture());
 }
diff --git a/shell/common/shell_test.h b/shell/common/shell_test.h
index 680db7d349c1d..9f02aa35e68b3 100644
--- a/shell/common/shell_test.h
+++ b/shell/common/shell_test.h
@@ -15,6 +15,7 @@
 #include "flutter/lib/ui/window/platform_message.h"
 #include "flutter/shell/common/run_configuration.h"
 #include "flutter/shell/common/shell.h"
+#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/thread_host.h"
 #include "flutter/shell/common/vsync_waiters_test.h"
 #include "flutter/testing/elf_loader.h"
@@ -31,9 +32,12 @@ class ShellTest : public ThreadTest {
   Settings CreateSettingsForFixture();
   std::unique_ptr<Shell> CreateShell(Settings settings,
                                      bool simulate_vsync = false);
-  std::unique_ptr<Shell> CreateShell(Settings settings,
-                                     TaskRunners task_runners,
-                                     bool simulate_vsync = false);
+  std::unique_ptr<Shell> CreateShell(
+      Settings settings,
+      TaskRunners task_runners,
+      bool simulate_vsync = false,
+      std::shared_ptr<ShellTestExternalViewEmbedder>
+          shell_test_external_view_embedder = nullptr);
   void DestroyShell(std::unique_ptr<Shell> shell);
   void DestroyShell(std::unique_ptr<Shell> shell, TaskRunners task_runners);
   TaskRunners GetTaskRunnersForFixture();
diff --git a/shell/common/shell_test_external_view_embedder.cc b/shell/common/shell_test_external_view_embedder.cc
new file mode 100644
index 0000000000000..683e21ad73c91
--- /dev/null
+++ b/shell/common/shell_test_external_view_embedder.cc
@@ -0,0 +1,55 @@
+#include "shell_test_external_view_embedder.h"
+
+namespace flutter {
+
+// |ExternalViewEmbedder|
+void ShellTestExternalViewEmbedder::CancelFrame() {}
+
+// |ExternalViewEmbedder|
+void ShellTestExternalViewEmbedder::BeginFrame(SkISize frame_size,
+                                               GrContext* context,
+                                               double device_pixel_ratio) {}
+
+// |ExternalViewEmbedder|
+void ShellTestExternalViewEmbedder::PrerollCompositeEmbeddedView(
+    int view_id,
+    std::unique_ptr<EmbeddedViewParams> params) {}
+
+// |ExternalViewEmbedder|
+PostPrerollResult ShellTestExternalViewEmbedder::PostPrerollAction(
+    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
+  FML_DCHECK(raster_thread_merger);
+  return post_preroll_result_;
+}
+
+// |ExternalViewEmbedder|
+std::vector<SkCanvas*> ShellTestExternalViewEmbedder::GetCurrentCanvases() {
+  return {};
+}
+
+// |ExternalViewEmbedder|
+SkCanvas* ShellTestExternalViewEmbedder::CompositeEmbeddedView(int view_id) {
+  return nullptr;
+}
+
+// |ExternalViewEmbedder|
+bool ShellTestExternalViewEmbedder::SubmitFrame(GrContext* context,
+                                                SkCanvas* background_canvas) {
+  return true;
+}
+
+// |ExternalViewEmbedder|
+void ShellTestExternalViewEmbedder::FinishFrame() {}
+
+// |ExternalViewEmbedder|
+void ShellTestExternalViewEmbedder::EndFrame(
+    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
+  end_frame_call_back_();
+}
+
+// |ExternalViewEmbedder|
+SkCanvas* ShellTestExternalViewEmbedder::GetRootCanvas() {
+  return nullptr;
+}
+
+}  // namespace flutter
diff --git a/shell/common/shell_test_external_view_embedder.h b/shell/common/shell_test_external_view_embedder.h
new file mode 100644
index 0000000000000..56d9123ea8a7a
--- /dev/null
+++ b/shell/common/shell_test_external_view_embedder.h
@@ -0,0 +1,72 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_SHELL_TEST_EXTERNAL_VIEW_EMBEDDER_H_
+#define FLUTTER_SHELL_TEST_EXTERNAL_VIEW_EMBEDDER_H_
+
+#include "flutter/flow/embedded_views.h"
+#include "flutter/fml/raster_thread_merger.h"
+
+namespace flutter {
+
+//------------------------------------------------------------------------------
+/// @brief The external view embedder used by |ShellTestPlatformViewGL|
+///
+class ShellTestExternalViewEmbedder final : public ExternalViewEmbedder {
+ public:
+  using EndFrameCallBack = std::function<void(void)>;
+
+  ShellTestExternalViewEmbedder(const EndFrameCallBack& end_frame_call_back,
+                                PostPrerollResult post_preroll_result)
+      : end_frame_call_back_(end_frame_call_back),
+        post_preroll_result_(post_preroll_result) {}
+
+  ~ShellTestExternalViewEmbedder() = default;
+
+ private:
+  // |ExternalViewEmbedder|
+  void CancelFrame() override;
+
+  // |ExternalViewEmbedder|
+  void BeginFrame(SkISize frame_size,
+                  GrContext* context,
+                  double device_pixel_ratio) override;
+
+  // |ExternalViewEmbedder|
+  void PrerollCompositeEmbeddedView(
+      int view_id,
+      std::unique_ptr<EmbeddedViewParams> params) override;
+
+  // |ExternalViewEmbedder|
+  PostPrerollResult PostPrerollAction(
+      fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) override;
+
+  // |ExternalViewEmbedder|
+  std::vector<SkCanvas*> GetCurrentCanvases() override;
+
+  // |ExternalViewEmbedder|
+  SkCanvas* CompositeEmbeddedView(int view_id) override;
+
+  // |ExternalViewEmbedder|
+  bool SubmitFrame(GrContext* context, SkCanvas* background_canvas) override;
+
+  // |ExternalViewEmbedder|
+  void FinishFrame() override;
+
+  // |ExternalViewEmbedder|
+  void EndFrame(
+      fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) override;
+
+  // |ExternalViewEmbedder|
+  SkCanvas* GetRootCanvas() override;
+
+  const EndFrameCallBack end_frame_call_back_;
+  const PostPrerollResult post_preroll_result_;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(ShellTestExternalViewEmbedder);
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_TEST_EXTERNAL_VIEW_EMBEDDER_H_
diff --git a/shell/common/shell_test_platform_view.cc b/shell/common/shell_test_platform_view.cc
index cfd43308bfc10..29bd24d3134ff 100644
--- a/shell/common/shell_test_platform_view.cc
+++ b/shell/common/shell_test_platform_view.cc
@@ -19,7 +19,9 @@ std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::Create(
     TaskRunners task_runners,
     std::shared_ptr<ShellTestVsyncClock> vsync_clock,
     CreateVsyncWaiter create_vsync_waiter,
-    BackendType backend) {
+    BackendType backend,
+    std::shared_ptr<ShellTestExternalViewEmbedder>
+        shell_test_external_view_embedder) {
   // TODO(gw280): https://github.com/flutter/flutter/issues/50298
   // Make this fully runtime configurable
   switch (backend) {
@@ -27,12 +29,14 @@ std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::Create(
 #ifdef SHELL_ENABLE_GL
     case BackendType::kGLBackend:
       return std::make_unique<ShellTestPlatformViewGL>(
-          delegate, task_runners, vsync_clock, create_vsync_waiter);
+          delegate, task_runners, vsync_clock, create_vsync_waiter,
+          shell_test_external_view_embedder);
 #endif  // SHELL_ENABLE_GL
 #ifdef SHELL_ENABLE_VULKAN
     case BackendType::kVulkanBackend:
       return std::make_unique<ShellTestPlatformViewVulkan>(
-          delegate, task_runners, vsync_clock, create_vsync_waiter);
+          delegate, task_runners, vsync_clock, create_vsync_waiter,
+          shell_test_external_view_embedder);
 #endif  // SHELL_ENABLE_VULKAN
     default:
       FML_LOG(FATAL) << "No backends supported for ShellTestPlatformView";
diff --git a/shell/common/shell_test_platform_view.h b/shell/common/shell_test_platform_view.h
index c7aefe86b33bc..9a850b1d481d6 100644
--- a/shell/common/shell_test_platform_view.h
+++ b/shell/common/shell_test_platform_view.h
@@ -6,6 +6,7 @@
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_H_
 
 #include "flutter/shell/common/platform_view.h"
+#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/vsync_waiters_test.h"
 
 namespace flutter {
@@ -24,7 +25,9 @@ class ShellTestPlatformView : public PlatformView {
       TaskRunners task_runners,
       std::shared_ptr<ShellTestVsyncClock> vsync_clock,
       CreateVsyncWaiter create_vsync_waiter,
-      BackendType backend);
+      BackendType backend,
+      std::shared_ptr<ShellTestExternalViewEmbedder>
+          shell_test_external_view_embedder);
 
   virtual void SimulateVSync() = 0;
 
diff --git a/shell/common/shell_test_platform_view_gl.cc b/shell/common/shell_test_platform_view_gl.cc
index 2bd597575e523..c980c53168645 100644
--- a/shell/common/shell_test_platform_view_gl.cc
+++ b/shell/common/shell_test_platform_view_gl.cc
@@ -12,11 +12,14 @@ ShellTestPlatformViewGL::ShellTestPlatformViewGL(
     PlatformView::Delegate& delegate,
     TaskRunners task_runners,
     std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-    CreateVsyncWaiter create_vsync_waiter)
+    CreateVsyncWaiter create_vsync_waiter,
+    std::shared_ptr<ShellTestExternalViewEmbedder>
+        shell_test_external_view_embedder)
     : ShellTestPlatformView(delegate, std::move(task_runners)),
       gl_surface_(SkISize::Make(800, 600)),
       create_vsync_waiter_(std::move(create_vsync_waiter)),
-      vsync_clock_(vsync_clock) {}
+      vsync_clock_(vsync_clock),
+      shell_test_external_view_embedder_(shell_test_external_view_embedder) {}
 
 ShellTestPlatformViewGL::~ShellTestPlatformViewGL() = default;
 
@@ -70,7 +73,7 @@ ShellTestPlatformViewGL::GetGLProcResolver() const {
 
 // |GPUSurfaceGLDelegate|
 ExternalViewEmbedder* ShellTestPlatformViewGL::GetExternalViewEmbedder() {
-  return nullptr;
+  return shell_test_external_view_embedder_.get();
 }
 
 }  // namespace testing
diff --git a/shell/common/shell_test_platform_view_gl.h b/shell/common/shell_test_platform_view_gl.h
index 03db7910873e0..cac2fdc649781 100644
--- a/shell/common/shell_test_platform_view_gl.h
+++ b/shell/common/shell_test_platform_view_gl.h
@@ -5,6 +5,7 @@
 #ifndef FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_GL_H_
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_GL_H_
 
+#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
 #include "flutter/shell/gpu/gpu_surface_gl_delegate.h"
 #include "flutter/testing/test_gl_surface.h"
@@ -18,7 +19,9 @@ class ShellTestPlatformViewGL : public ShellTestPlatformView,
   ShellTestPlatformViewGL(PlatformView::Delegate& delegate,
                           TaskRunners task_runners,
                           std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-                          CreateVsyncWaiter create_vsync_waiter);
+                          CreateVsyncWaiter create_vsync_waiter,
+                          std::shared_ptr<ShellTestExternalViewEmbedder>
+                              shell_test_external_view_embedder);
 
   virtual ~ShellTestPlatformViewGL() override;
 
@@ -31,6 +34,9 @@ class ShellTestPlatformViewGL : public ShellTestPlatformView,
 
   std::shared_ptr<ShellTestVsyncClock> vsync_clock_;
 
+  std::shared_ptr<ShellTestExternalViewEmbedder>
+      shell_test_external_view_embedder_;
+
   // |PlatformView|
   std::unique_ptr<Surface> CreateRenderingSurface() override;
 
diff --git a/shell/common/shell_test_platform_view_vulkan.cc b/shell/common/shell_test_platform_view_vulkan.cc
index e9f41484d9881..4c21c2dfba36e 100644
--- a/shell/common/shell_test_platform_view_vulkan.cc
+++ b/shell/common/shell_test_platform_view_vulkan.cc
@@ -11,11 +11,14 @@ ShellTestPlatformViewVulkan::ShellTestPlatformViewVulkan(
     PlatformView::Delegate& delegate,
     TaskRunners task_runners,
     std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-    CreateVsyncWaiter create_vsync_waiter)
+    CreateVsyncWaiter create_vsync_waiter,
+    std::shared_ptr<ShellTestExternalViewEmbedder>
+        shell_test_external_view_embedder)
     : ShellTestPlatformView(delegate, std::move(task_runners)),
       create_vsync_waiter_(std::move(create_vsync_waiter)),
       vsync_clock_(vsync_clock),
-      proc_table_(fml::MakeRefCounted<vulkan::VulkanProcTable>()) {}
+      proc_table_(fml::MakeRefCounted<vulkan::VulkanProcTable>()),
+      shell_test_external_view_embedder_(shell_test_external_view_embedder) {}
 
 ShellTestPlatformViewVulkan::~ShellTestPlatformViewVulkan() = default;
 
@@ -29,7 +32,8 @@ void ShellTestPlatformViewVulkan::SimulateVSync() {
 
 // |PlatformView|
 std::unique_ptr<Surface> ShellTestPlatformViewVulkan::CreateRenderingSurface() {
-  return std::make_unique<OffScreenSurface>(proc_table_);
+  return std::make_unique<OffScreenSurface>(proc_table_,
+                                            shell_test_external_view_embedder_);
 }
 
 // |PlatformView|
@@ -44,8 +48,12 @@ PointerDataDispatcherMaker ShellTestPlatformViewVulkan::GetDispatcherMaker() {
 //              We need to merge this functionality back into //vulkan.
 //              https://github.com/flutter/flutter/issues/51132
 ShellTestPlatformViewVulkan::OffScreenSurface::OffScreenSurface(
-    fml::RefPtr<vulkan::VulkanProcTable> vk)
-    : valid_(false), vk_(std::move(vk)) {
+    fml::RefPtr<vulkan::VulkanProcTable> vk,
+    std::shared_ptr<ShellTestExternalViewEmbedder>
+        shell_test_external_view_embedder)
+    : valid_(false),
+      vk_(std::move(vk)),
+      shell_test_external_view_embedder_(shell_test_external_view_embedder) {
   if (!vk_ || !vk_->HasAcquiredMandatoryProcAddresses()) {
     FML_DLOG(ERROR) << "Proc table has not acquired mandatory proc addresses.";
     return;
@@ -170,5 +178,10 @@ SkMatrix ShellTestPlatformViewVulkan::OffScreenSurface::GetRootTransformation()
   return matrix;
 }
 
+flutter::ExternalViewEmbedder*
+ShellTestPlatformViewVulkan::OffScreenSurface::GetExternalViewEmbedder() {
+  return shell_test_external_view_embedder_.get();
+}
+
 }  // namespace testing
 }  // namespace flutter
diff --git a/shell/common/shell_test_platform_view_vulkan.h b/shell/common/shell_test_platform_view_vulkan.h
index 38bce87fa5414..31757f39a30b0 100644
--- a/shell/common/shell_test_platform_view_vulkan.h
+++ b/shell/common/shell_test_platform_view_vulkan.h
@@ -5,6 +5,7 @@
 #ifndef FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_VULKAN_H_
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_VULKAN_H_
 
+#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
 #include "flutter/shell/gpu/gpu_surface_vulkan_delegate.h"
 #include "flutter/vulkan/vulkan_application.h"
@@ -18,7 +19,9 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
   ShellTestPlatformViewVulkan(PlatformView::Delegate& delegate,
                               TaskRunners task_runners,
                               std::shared_ptr<ShellTestVsyncClock> vsync_clock,
-                              CreateVsyncWaiter create_vsync_waiter);
+                              CreateVsyncWaiter create_vsync_waiter,
+                              std::shared_ptr<ShellTestExternalViewEmbedder>
+                                  shell_test_external_view_embedder);
 
   ~ShellTestPlatformViewVulkan() override;
 
@@ -27,7 +30,9 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
  private:
   class OffScreenSurface : public flutter::Surface {
    public:
-    OffScreenSurface(fml::RefPtr<vulkan::VulkanProcTable> vk);
+    OffScreenSurface(fml::RefPtr<vulkan::VulkanProcTable> vk,
+                     std::shared_ptr<ShellTestExternalViewEmbedder>
+                         shell_test_external_view_embedder);
 
     ~OffScreenSurface() override;
 
@@ -42,9 +47,13 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
     // |Surface|
     GrContext* GetContext() override;
 
+    flutter::ExternalViewEmbedder* GetExternalViewEmbedder() override;
+
    private:
     bool valid_;
     fml::RefPtr<vulkan::VulkanProcTable> vk_;
+    std::shared_ptr<ShellTestExternalViewEmbedder>
+        shell_test_external_view_embedder_;
     std::unique_ptr<vulkan::VulkanApplication> application_;
     std::unique_ptr<vulkan::VulkanDevice> logical_device_;
     sk_sp<GrContext> context_;
@@ -61,6 +70,9 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
 
   fml::RefPtr<vulkan::VulkanProcTable> proc_table_;
 
+  std::shared_ptr<ShellTestExternalViewEmbedder>
+      shell_test_external_view_embedder_;
+
   // |PlatformView|
   std::unique_ptr<Surface> CreateRenderingSurface() override;
 
diff --git a/shell/common/shell_unittests.cc b/shell/common/shell_unittests.cc
index c9c1345541fcc..720666ae1bb69 100644
--- a/shell/common/shell_unittests.cc
+++ b/shell/common/shell_unittests.cc
@@ -23,6 +23,7 @@
 #include "flutter/shell/common/platform_view.h"
 #include "flutter/shell/common/rasterizer.h"
 #include "flutter/shell/common/shell_test.h"
+#include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
 #include "flutter/shell/common/switches.h"
 #include "flutter/shell/common/thread_host.h"
@@ -139,7 +140,7 @@ TEST_F(ShellTest,
               return static_cast<std::unique_ptr<VsyncWaiter>>(
                   std::make_unique<VsyncWaiterFallback>(task_runners));
             },
-            ShellTestPlatformView::BackendType::kDefaultBackend);
+            ShellTestPlatformView::BackendType::kDefaultBackend, nullptr);
       },
       [](Shell& shell) {
         return std::make_unique<Rasterizer>(shell, shell.GetTaskRunners());
@@ -466,6 +467,51 @@ TEST_F(ShellTest, FrameRasterizedCallbackIsCalled) {
   DestroyShell(std::move(shell));
 }
 
+TEST_F(ShellTest,
+       ExternalEmbedderEndFrameIsCalledWhenPostPrerollResultIsResubmit) {
+  auto settings = CreateSettingsForFixture();
+  fml::AutoResetWaitableEvent endFrameLatch;
+  bool end_frame_called = false;
+  auto end_frame_callback = [&] {
+    end_frame_called = true;
+    endFrameLatch.Signal();
+  };
+  auto external_view_embedder = std::make_shared<ShellTestExternalViewEmbedder>(
+      end_frame_callback, PostPrerollResult::kResubmitFrame);
+  auto shell = CreateShell(std::move(settings), GetTaskRunnersForFixture(),
+                           false, external_view_embedder);
+
+  // Create the surface needed by rasterizer
+  PlatformViewNotifyCreated(shell.get());
+
+  auto configuration = RunConfiguration::InferFromSettings(settings);
+  configuration.SetEntrypoint("emptyMain");
+
+  RunEngine(shell.get(), std::move(configuration));
+
+  LayerTreeBuilder builder = [&](std::shared_ptr<ContainerLayer> root) {
+    SkPictureRecorder recorder;
+    SkCanvas* recording_canvas =
+        recorder.beginRecording(SkRect::MakeXYWH(0, 0, 80, 80));
+    recording_canvas->drawRect(SkRect::MakeXYWH(0, 0, 80, 80),
+                               SkPaint(SkColor4f::FromColor(SK_ColorRED)));
+    auto sk_picture = recorder.finishRecordingAsPicture();
+    fml::RefPtr<SkiaUnrefQueue> queue = fml::MakeRefCounted<SkiaUnrefQueue>(
+        this->GetCurrentTaskRunner(), fml::TimeDelta::FromSeconds(0));
+    auto picture_layer = std::make_shared<PictureLayer>(
+        SkPoint::Make(10, 10),
+        flutter::SkiaGPUObject<SkPicture>({sk_picture, queue}), false, false);
+    root->Add(picture_layer);
+  };
+
+  PumpOneFrame(shell.get(), 100, 100, builder);
+  endFrameLatch.Wait();
+
+  ASSERT_TRUE(end_frame_called);
+
+  DestroyShell(std::move(shell));
+}
+
 TEST(SettingsTest, FrameTimingSetsAndGetsProperly) {
   // Ensure that all phases are in kPhases.
   ASSERT_EQ(sizeof(FrameTiming::kPhases),
diff --git a/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm b/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm
index 3fbaa7dd8a935..2c2a91f4836a6 100644
--- a/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm
+++ b/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm
@@ -248,7 +248,7 @@
 }
 
 void FlutterPlatformViewsController::CancelFrame() {
-  composition_order_.clear();
+  composition_order_ = active_composition_order_;
 }
 
 bool FlutterPlatformViewsController::HasPendingViewOperations() {
@@ -267,8 +267,9 @@
     if (raster_thread_merger->IsMerged()) {
       raster_thread_merger->ExtendLeaseTo(kDefaultMergedLeaseDuration);
     } else {
+      // Wait until |EndFrame| to merge the threads.
+      merge_threads_ = true;
       CancelFrame();
-      raster_thread_merger->MergeWithLease(kDefaultMergedLeaseDuration);
       return PostPrerollResult::kResubmitFrame;
     }
   }
@@ -468,6 +469,21 @@
 bool FlutterPlatformViewsController::SubmitFrame(GrContext* gr_context,
                                                  std::shared_ptr<IOSContext> ios_context,
                                                  SkCanvas* background_canvas) {
+  if (merge_threads_) {
+    // Threads are about to be merged, we drop everything from this frame
+    // and possibly resubmit the same layer tree in the next frame.
+    // Before merging thread, we know the code is not running on the main thread. Assert that
+    FML_DCHECK(![[NSThread currentThread] isMainThread]);
+    picture_recorders_.clear();
+    composition_order_.clear();
+    return true;
+  }
+
+  // Any UIKit related code has to run on main thread.
+  // When on a non-main thread, we only allow the rest of the method to run if there is no platform
+  // view.
+  FML_DCHECK([[NSThread currentThread] isMainThread] || views_to_dispose_.empty());
+
   DisposeViews();
 
   // Resolve all pending GPU operations before allocating a new surface.
@@ -578,6 +594,14 @@
   }
 }
 
+void FlutterPlatformViewsController::EndFrame(
+    fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
+  if (merge_threads_) {
+    raster_thread_merger->MergeWithLease(kDefaultMergedLeaseDuration);
+    merge_threads_ = false;
+  }
+}
+
 std::shared_ptr<FlutterPlatformViewLayer> FlutterPlatformViewsController::GetLayer(
     GrContext* gr_context,
     std::shared_ptr<IOSContext> ios_context,
@@ -642,6 +666,8 @@
     return;
   }
 
+  FML_DCHECK([[NSThread currentThread] isMainThread]);
+
   for (int64_t viewId : views_to_dispose_) {
     UIView* root_view = root_views_[viewId].get();
     [root_view removeFromSuperview];
diff --git a/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h b/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h
index e998640777c96..6532be8ca14c2 100644
--- a/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h
+++ b/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h
@@ -134,6 +134,8 @@ class FlutterPlatformViewsController {
 
   void SetFrameSize(SkISize frame_size);
 
+  // Indicates that we don't compisite any platform views or overlays during this frame.
+  // Also reverts the composition_order_ to its original state at the begining of the frame.
   void CancelFrame();
 
   void PrerollCompositeEmbeddedView(int view_id,
@@ -163,6 +165,11 @@ class FlutterPlatformViewsController {
                    std::shared_ptr<IOSContext> ios_context,
                    SkCanvas* background_canvas);
 
+  // Invoked at the very end of a frame.
+  // After invoking this method, nothing should happen on the current TaskRunner during the same
+  // frame.
+  void EndFrame(fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger);
+
   void OnMethodCall(FlutterMethodCall* call, FlutterResult& result);
 
  private:
@@ -273,6 +280,10 @@ class FlutterPlatformViewsController {
   void ApplyMutators(const MutatorsStack& mutators_stack, UIView* embedded_view);
   void CompositeWithParams(int view_id, const EmbeddedViewParams& params);
 
+  // Default to `false`.
+  // If `true`, gpu thread and platform thread should be merged during |EndFrame|.
+  // Always resets to `false` right after the threads are merged.
+  bool merge_threads_;
   // Allocates a new FlutterPlatformViewLayer if needed, draws the pixels within the rect from
   // the picture on the layer's canvas.
   std::shared_ptr<FlutterPlatformViewLayer> GetLayer(GrContext* gr_context,
@@ -282,6 +293,7 @@ class FlutterPlatformViewsController {
                                                      int64_t view_id,
                                                      int64_t overlay_id);
   // Removes overlay views and platform views that aren't needed in the current frame.
+  // Must run on the platform thread.
   void RemoveUnusedLayers();
   // Appends the overlay views and platform view and sets their z index based on the composition
   // order.
diff --git a/shell/platform/darwin/ios/ios_surface.h b/shell/platform/darwin/ios/ios_surface.h
index fd1bc7abb0b48..eae39031d77ce 100644
--- a/shell/platform/darwin/ios/ios_surface.h
+++ b/shell/platform/darwin/ios/ios_surface.h
@@ -83,6 +83,9 @@ class IOSSurface : public ExternalViewEmbedder {
   // |ExternalViewEmbedder|
   void FinishFrame() override;
 
+  // |ExternalViewEmbedder|
+  void EndFrame(fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) override;
+
  public:
   FML_DISALLOW_COPY_AND_ASSIGN(IOSSurface);
 };
diff --git a/shell/platform/darwin/ios/ios_surface.mm b/shell/platform/darwin/ios/ios_surface.mm
index cbe2cb4fb8c2c..5f2725273e0dd 100644
--- a/shell/platform/darwin/ios/ios_surface.mm
+++ b/shell/platform/darwin/ios/ios_surface.mm
@@ -90,7 +90,12 @@ bool IsIosEmbeddedViewsPreviewEnabled() {
   platform_views_controller_->CancelFrame();
   // Committing the current transaction as |BeginFrame| will create a nested
   // CATransaction otherwise.
-  [CATransaction commit];
+  if ([[NSThread currentThread] isMainThread]) {
+    // The only time we need to commit the `CATranscation` is when
+    // there are platform views in the scene, which has to be run on the
+    // main thread.
+    [CATransaction commit];
+  }
 }
 
 // |ExternalViewEmbedder|
@@ -98,7 +103,12 @@ bool IsIosEmbeddedViewsPreviewEnabled() {
   TRACE_EVENT0("flutter", "IOSSurface::BeginFrame");
   FML_CHECK(platform_views_controller_ != nullptr);
   platform_views_controller_->SetFrameSize(frame_size);
-  [CATransaction begin];
+  if ([[NSThread currentThread] isMainThread]) {
+    // The only time we need to commit the `CATranscation` is when
+    // there are platform views in the scene, which has to be run on the
+    // main thread.
+    [CATransaction begin];
+  }
 }
 
 // |ExternalViewEmbedder|
@@ -140,10 +150,22 @@ bool IsIosEmbeddedViewsPreviewEnabled() {
   return submitted;
 }
 
+// |ExternalViewEmbedder|
+void IOSSurface::EndFrame(fml::RefPtr<fml::RasterThreadMerger> raster_thread_merger) {
+  TRACE_EVENT0("flutter", "IOSSurface::EndFrame");
+  FML_CHECK(platform_views_controller_ != nullptr);
+  return platform_views_controller_->EndFrame(raster_thread_merger);
+}
+
 // |ExternalViewEmbedder|
 void IOSSurface::FinishFrame() {
   TRACE_EVENT0("flutter", "IOSSurface::DidSubmitFrame");
+  if (![[NSThread currentThread] isMainThread]) {
+    return;
+  }
+  // The only time we need to commit the `CATranscation` is when
+  // there are platform views in the scene, which has to be run on the
+  // main thread.
   [CATransaction commit];
 }
-
 }  // namespace flutter