cc: Add receiver for CompositorFrameAck in LayerTreeHostImpl and forward it to the renderer.

cc/renderer.h

Index: cc/renderer.h
diff --git a/cc/renderer.h b/cc/renderer.h
index b739537484b1e3bed053b44b963dd06d1b3c2c26..981679cc08826f942e6e2a17d8ba421f9a64aaf1 100644
--- a/cc/renderer.h
+++ b/cc/renderer.h
@@ -13,6 +13,7 @@
 
 namespace cc {
 
+class CompositorFrameAck;
 class ScopedResource;
 
 class CC_EXPORT RendererClient {
@@ -49,6 +50,7 @@ public:
     int viewportHeight() { return viewportSize().height(); }
 
     virtual void viewportChanged() { }
+    virtual void receiveCompositorFrameAck(const CompositorFrameAck&) { }
 
     virtual void decideRenderPassAllocationsForFrame(const RenderPassList&) { }
     virtual bool haveCachedResourcesForRenderPassId(RenderPass::Id) const;