cc: Add OutputSurface state snapshots.

cc/output/output_surface_client.h

Index: cc/output/output_surface_client.h
diff --git a/cc/output/output_surface_client.h b/cc/output/output_surface_client.h
index 7f8cadef43b73d9c299d1081c887976cacd8ab54..f5a81944c109d59c7d605ad9a6edbf1437744d88 100644
--- a/cc/output/output_surface_client.h
+++ b/cc/output/output_surface_client.h
@@ -12,6 +12,7 @@
 #include "cc/output/context_provider.h"
 #include "cc/resources/returned_resource.h"
 #include "gpu/command_buffer/common/texture_in_use_response.h"
+#include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
@@ -29,6 +30,11 @@ class CC_EXPORT OutputSurfaceClient {
   virtual void DidReceiveTextureInUseResponses(
       const gpu::TextureInUseResponses& responses) = 0;
 
+  // Readback the contents of last swapped overlay textures.
+  virtual void ReadbackSwappedOverlayTextures(
+      std::vector<SkBitmap>* bitmaps,
+      const base::Callback<void(bool)>& callback) = 0;
+
  protected:
   virtual ~OutputSurfaceClient() {}
 };