cc: Cleanup class/struct forward declarations

cc/test/test_hooks.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TEST_TEST_HOOKS_H_
 #define CC_TEST_TEST_HOOKS_H_
 
 #include "base/macros.h"
 #include "cc/animation/animation_delegate.h"
 #include "cc/trees/layer_tree_host.h"
 #include "cc/trees/layer_tree_host_impl.h"
 
 namespace cc {
 
 class CompositorFrame;
 
-namespace proto {
-class CompositorMessageToImpl;
-}
-
 // Used by test stubs to notify the test when something interesting happens.
 class TestHooks : public AnimationDelegate {
  public:
   TestHooks();
   ~TestHooks() override;
 
   // Compositor thread hooks.
   virtual void CreateResourceAndRasterBufferProvider(
       LayerTreeHostImpl* host_impl,
       std::unique_ptr<RasterBufferProvider>* raster_buffer_provider,
@@ skipping 85 matching lines @@
   // OutputSurface indirections to the LayerTreeTest, that can be further
   // overridden.
   virtual void RequestNewCompositorFrameSink() = 0;
   virtual std::unique_ptr<OutputSurface> CreateDisplayOutputSurfaceOnThread(
       scoped_refptr<ContextProvider> compositor_context_provider) = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_TEST_HOOKS_H_