Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 9797c974b27798cd7a65185f67220914cb8220ad..80c2e596d5e4f1554eadd8fd3b52f9ab137a98f9 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1095,8 +1095,7 @@ void LayerTreeHostImpl::RemoveRenderPasses(RenderPassCuller culler,
 }
 
 DrawSwapReadbackResult::DrawResult LayerTreeHostImpl::PrepareToDraw(
-    FrameData* frame,
-    const gfx::Rect& damage_rect) {
+    FrameData* frame) {
   TRACE_EVENT1("cc",
                "LayerTreeHostImpl::PrepareToDraw",
                "SourceFrameNumber",
@@ -1117,9 +1116,8 @@ DrawSwapReadbackResult::DrawResult LayerTreeHostImpl::PrepareToDraw(
   frame->contains_incomplete_tile = false;
   frame->has_no_damage = false;
 
-  gfx::Rect device_viewport_damage_rect(damage_rect);
   if (active_tree_->root_layer()) {
-    device_viewport_damage_rect.Union(viewport_damage_rect_);
+    gfx::Rect device_viewport_damage_rect = viewport_damage_rect_;
     viewport_damage_rect_ = gfx::Rect();
 
     active_tree_->root_layer()->render_surface()->damage_tracker()->
@@ -1615,12 +1613,6 @@ void LayerTreeHostImpl::DidLoseOutputSurface() {
 #endif
 }
 
-void LayerTreeHostImpl::Readback(void* pixels,
-                                 const gfx::Rect& rect_in_device_viewport) {
-  DCHECK(renderer_);
-  renderer_->GetFramebufferPixels(pixels, rect_in_device_viewport);
-}
-
 bool LayerTreeHostImpl::HaveRootScrollLayer() const {
   return !!InnerViewportScrollLayer();
 }