Use WebKit compositor in ui::Layer

ui/gfx/compositor/compositor.cc

Index: ui/gfx/compositor/compositor.cc
diff --git a/ui/gfx/compositor/compositor.cc b/ui/gfx/compositor/compositor.cc
index 6f7e5dba2a6ede01509996fb250dc7ca6d7125e7..87aa06eccfa58951760db8e1a4439e004419554b 100644
--- a/ui/gfx/compositor/compositor.cc
+++ b/ui/gfx/compositor/compositor.cc
@@ -25,10 +25,15 @@ Compositor::Compositor(CompositorDelegate* delegate, const gfx::Size& size)
 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) {
@@ -36,7 +41,7 @@ void Compositor::Draw(bool force_clear) {
     return;
 
   NotifyStart(force_clear);
-  root_layer_->DrawTree();
+  DrawTree();
   NotifyEnd();
 }
 
@@ -52,6 +57,14 @@ 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);
 }