Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/output/delegating_renderer.h

Index: cc/output/delegating_renderer.h
diff --git a/cc/output/delegating_renderer.h b/cc/output/delegating_renderer.h
index 991ae00dcf7445c2ba65745f48fe233b7c334672..2649bcbf30315ec454c105fb9197b76c24dc4134 100644
--- a/cc/output/delegating_renderer.h
+++ b/cc/output/delegating_renderer.h
@@ -26,8 +26,6 @@ class CC_EXPORT DelegatingRenderer : public Renderer {
 
   virtual const RendererCapabilitiesImpl& Capabilities() const OVERRIDE;
 
-  virtual bool CanReadPixels() const OVERRIDE;
-
   virtual void DrawFrame(RenderPassList* render_passes_in_draw_order,
                          float device_scale_factor,
                          const gfx::Rect& device_viewport_rect,
@@ -39,9 +37,6 @@ class CC_EXPORT DelegatingRenderer : public Renderer {
   virtual void SwapBuffers(const CompositorFrameMetadata& metadata) OVERRIDE;
   virtual void ReceiveSwapBuffersAck(const CompositorFrameAck&) OVERRIDE;
 
-  virtual void GetFramebufferPixels(void* pixels,
-                                    const gfx::Rect& rect) OVERRIDE;
-
   virtual bool IsContextLost() OVERRIDE;
 
   virtual void SendManagedMemoryStats(size_t bytes_visible,