Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/output/delegating_renderer.cc

Index: cc/output/delegating_renderer.cc
diff --git a/cc/output/delegating_renderer.cc b/cc/output/delegating_renderer.cc
index 90ff409e4907c95d168f4f9eff84e573cf9f270c..e3b7c6889ea9290214a2a22798129d51c599c461 100644
--- a/cc/output/delegating_renderer.cc
+++ b/cc/output/delegating_renderer.cc
@@ -75,8 +75,6 @@ const RendererCapabilitiesImpl& DelegatingRenderer::Capabilities() const {
   return capabilities_;
 }
 
-bool DelegatingRenderer::CanReadPixels() const { return false; }
-
 static ResourceProvider::ResourceId AppendToArray(
     ResourceProvider::ResourceIdArray* array,
     ResourceProvider::ResourceId id) {
@@ -118,11 +116,6 @@ void DelegatingRenderer::SwapBuffers(const CompositorFrameMetadata& metadata) {
   output_surface_->SwapBuffers(&compositor_frame);
 }
 
-void DelegatingRenderer::GetFramebufferPixels(void* pixels,
-                                              const gfx::Rect& rect) {
-  NOTREACHED();
-}
-
 void DelegatingRenderer::ReceiveSwapBuffersAck(
     const CompositorFrameAck& ack) {
   resource_provider_->ReceiveReturnsFromParent(ack.resources);