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 9f55fc3fa3d0ba72a1c7f673e5e67416ba1556b8..63c68d2cea5dd6006d85951c0c33f6a16738d2ad 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 gfx {
@@ -36,6 +37,11 @@ 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,

[danakj, 2016/11/01 23:33:01]

why not a parameter of the Callback?

[reveman, 2016/11/02 00:37:05]

It just evolved this way. I guess the alternative is to pass
std::unique_ptr<std::vector<SkBitmap>> with this callback and
std::unique_ptr<SkBitmap> with the framebuffer version but it seemed a bit
easier to just allocate these objects upfront and the buffer queue and
outputsurface fill them in. Let me know if you prefer that or have a better idea
for how to do this.

+      const base::Callback<void(bool)>& callback) = 0;
+
  protected:
   virtual ~OutputSurfaceClient() {}
 };