Use WebKit compositor in ui::Layer

ui/gfx/compositor/compositor.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/compositor/compositor.h"
 
 #include "ui/gfx/compositor/compositor_observer.h"
 #include "ui/gfx/compositor/layer.h"
 
 namespace ui {
 
 TextureDrawParams::TextureDrawParams()
     : blend(false),
       has_valid_alpha_channel(false),
       opacity(1.0f),
       vertically_flipped(false) {
 }
 
 Compositor::Compositor(CompositorDelegate* delegate, const gfx::Size& size)
     : delegate_(delegate),
       size_(size),
       root_layer_(NULL) {
 }
 
 Compositor::~Compositor() {
 }
 
+void Compositor::ScheduleDraw() {
+  delegate_->ScheduleDraw();
+}
+
 void Compositor::SetRootLayer(Layer* root_layer) {
   root_layer_ = root_layer;
   if (!root_layer_->GetCompositor())
     root_layer_->SetCompositor(this);
+  OnRootLayerChanged();
 }
 
 void Compositor::Draw(bool force_clear) {
   if (!root_layer_)
     return;
 
   NotifyStart(force_clear);
-  root_layer_->DrawTree();
+  DrawTree();
   NotifyEnd();
 }
 
 void Compositor::AddObserver(CompositorObserver* observer) {
   observer_list_.AddObserver(observer);
 }
 
 void Compositor::RemoveObserver(CompositorObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
 bool Compositor::HasObserver(CompositorObserver* observer) {
   return observer_list_.HasObserver(observer);
 }
 
+void Compositor::OnRootLayerChanged() {
+  ScheduleDraw();
+}
+
+void Compositor::DrawTree() {
+  root_layer_->DrawTree();
+}
+
 void Compositor::NotifyStart(bool clear) {
   OnNotifyStart(clear);
 }
 
 void Compositor::NotifyEnd() {
   OnNotifyEnd();
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));
 }
 
 }  // namespace ui