[scenarios] test disabling surface clear.

shell/platform/android/io/flutter/embedding/engine/renderer/FlutterRenderer.java

@@ -62,6 +62,9 @@ public class FlutterRenderer implements TextureRegistry {
    */
   @VisibleForTesting public static boolean debugForceSurfaceProducerGlTextures = false;
 
+  /** Whether to disable clearing of the Surface used to render platform views. */
+  @VisibleForTesting public static boolean debugDisableSurfaceClear = false;
+
   private static final String TAG = "FlutterRenderer";
 
   @NonNull private final FlutterJNI flutterJNI;

shell/platform/android/io/flutter/plugin/platform/PlatformViewWrapper.java

@@ -26,6 +26,7 @@
 import androidx.annotation.VisibleForTesting;
 import io.flutter.Log;
 import io.flutter.embedding.android.AndroidTouchProcessor;
+import io.flutter.embedding.engine.renderer.FlutterRenderer;
 import io.flutter.util.ViewUtils;
 
 /**
@@ -63,7 +64,7 @@ public PlatformViewWrapper(
     this.renderTarget = renderTarget;
 
     Surface surface = renderTarget.getSurface();
-    if (surface != null) {
+    if (surface != null && !FlutterRenderer.debugDisableSurfaceClear) {
       final Canvas canvas = surface.lockHardwareCanvas();
       try {
         canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);

testing/scenario_app/android/app/src/androidTest/java/dev/flutter/TestRunner.java

@@ -24,6 +24,7 @@ public void onCreate(@Nullable Bundle arguments) {
             "--impeller-backend=" + arguments.getString("impeller-backend", "vulkan")
           };
     }
+    FlutterRenderer.debugDisableSurfaceClear = true;
     if ("true".equals(arguments.getString("force-surface-producer-surface-texture"))) {
       // Set a test flag to force the SurfaceProducer to use SurfaceTexture.
       FlutterRenderer.debugForceSurfaceProducerGlTextures = true;