Use surface copy requests for layout tests.

cc/test/test_delegating_output_surface.h

Index: cc/test/test_delegating_output_surface.h
diff --git a/cc/test/test_delegating_output_surface.h b/cc/test/test_delegating_output_surface.h
index cf7a32b4fc0fc8b4acd250af6ea06b11b0bc770b..718116fc0b45c30e4242667e70299f81264d21b1 100644
--- a/cc/test/test_delegating_output_surface.h
+++ b/cc/test/test_delegating_output_surface.h
@@ -18,6 +18,8 @@
 
 namespace cc {
 
+class CopyOutputRequest;
+
 class TestDelegatingOutputSurface : public OutputSurface,
                                     public SurfaceFactoryClient,
                                     public DisplayClient {
@@ -35,6 +37,9 @@ class TestDelegatingOutputSurface : public OutputSurface,
 
   Display* display() const { return display_.get(); }
 
+  // Will be submitted with the next SwapBuffers.
+  void RequestCopyOfOutput(std::unique_ptr<CopyOutputRequest> request);
+
   // OutputSurface implementation.
   bool BindToClient(OutputSurfaceClient* client) override;
   void DetachFromClient() override;
@@ -68,6 +73,8 @@ class TestDelegatingOutputSurface : public OutputSurface,
 
   bool bound_ = false;
 
+  std::vector<std::unique_ptr<CopyOutputRequest>> copy_requests_;
+
   base::WeakPtrFactory<TestDelegatingOutputSurface> weak_ptrs_;
 };