Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/output/renderer.h

Index: cc/output/renderer.h
diff --git a/cc/output/renderer.h b/cc/output/renderer.h
index 99cc6286e00ac0fd33172405cfadb602a909a74c..c70220980842de7cf1341fa7b3b75d78437a7c32 100644
--- a/cc/output/renderer.h
+++ b/cc/output/renderer.h
@@ -48,8 +48,6 @@ class CC_EXPORT Renderer {
 
   virtual const RendererCapabilitiesImpl& Capabilities() const = 0;
 
-  virtual bool CanReadPixels() const = 0;
-
   virtual void DecideRenderPassAllocationsForFrame(
       const RenderPassList& render_passes_in_draw_order) {}
   virtual bool HasAllocatedResourcesForTesting(RenderPass::Id id) const;
@@ -74,8 +72,6 @@ class CC_EXPORT Renderer {
   virtual void SwapBuffers(const CompositorFrameMetadata& metadata) = 0;
   virtual void ReceiveSwapBuffersAck(const CompositorFrameAck& ack) {}
 
-  virtual void GetFramebufferPixels(void* pixels, const gfx::Rect& rect) = 0;
-
   virtual bool IsContextLost();
 
   bool visible() const { return visible_; }