[Impeller] Remove additional shader bootstrap. (#52368)

Because these shaders must first acquire the prototype shader, it causes ContentContext creation to block. We can re-explore dealing with PSO generation in a different manner that isn't on the startup fast path.

flutter/flutter#143540

Author: jonahwilliams

impeller/entity/contents/content_context.cc

@@ -271,9 +271,6 @@ ContentContext::ContentContext(
   checkerboard_pipelines_.CreateDefault(*context_, options);
 #endif  // IMPELLER_DEBUG
 
-  // These pipelines are created first since they are immediately used by
-  // InitializeCommonlyUsedShadersIfNeeded. Their order matches the order in
-  // InitializeCommonlyUsedShadersIfNeeded.
   {
     solid_fill_pipelines_.CreateDefault(*context_, options);
     texture_pipelines_.CreateDefault(*context_, options);
@@ -571,48 +568,6 @@ void ContentContext::InitializeCommonlyUsedShadersIfNeeded() const {
   TRACE_EVENT0("flutter", "InitializeCommonlyUsedShadersIfNeeded");
   GetContext()->InitializeCommonlyUsedShadersIfNeeded();
 
-  if (GetContext()->GetBackendType() == Context::BackendType::kOpenGLES) {
-    // TODO(jonahwilliams): The OpenGL Embedder Unittests hang if this code
-    // runs.
-    return;
-  }
-
-  // Initialize commonly used shaders that aren't defaults. These settings were
-  // chosen based on the knowledge that we mix and match triangle and
-  // triangle-strip geometry, and also have fairly agressive srcOver to src
-  // blend mode conversions.
-  auto options = ContentContextOptions{
-      .sample_count = SampleCount::kCount4,
-      .color_attachment_pixel_format =
-          context_->GetCapabilities()->GetDefaultColorFormat()};
-
-  // Note: When editing this, check the order the default pipelines are created.
-  // These should be first.
-  for (const auto mode : {BlendMode::kSource, BlendMode::kSourceOver}) {
-    for (const auto geometry :
-         {PrimitiveType::kTriangle, PrimitiveType::kTriangleStrip}) {
-      options.blend_mode = mode;
-      options.primitive_type = geometry;
-      CreateIfNeeded(solid_fill_pipelines_, options);
-      CreateIfNeeded(texture_pipelines_, options);
-      if (GetContext()->GetCapabilities()->SupportsSSBO()) {
-        CreateIfNeeded(linear_gradient_ssbo_fill_pipelines_, options);
-        CreateIfNeeded(radial_gradient_ssbo_fill_pipelines_, options);
-        CreateIfNeeded(sweep_gradient_ssbo_fill_pipelines_, options);
-        CreateIfNeeded(conical_gradient_ssbo_fill_pipelines_, options);
-      }
-    }
-  }
-
-  options.blend_mode = BlendMode::kDestination;
-  options.primitive_type = PrimitiveType::kTriangleStrip;
-  for (const auto stencil_mode :
-       {ContentContextOptions::StencilMode::kOverdrawPreventionIncrement,
-        ContentContextOptions::StencilMode::kOverdrawPreventionRestore}) {
-    options.stencil_mode = stencil_mode;
-    CreateIfNeeded(clip_pipelines_, options);
-  }
-
   // On ARM devices, the initial usage of vkCmdCopyBufferToImage has been
   // observed to take 10s of ms as an internal shader is compiled to perform
   // the operation. Similarly, the initial render pass can also take 10s of ms