Clean up ui<->cc layers interface.

ui/compositor/compositor.cc

 // Copyright (c) 2012 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/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
@@ skipping 144 matching lines @@
 
   CancelCompositorLock();
   DCHECK(!compositor_lock_);
 
   FOR_EACH_OBSERVER(CompositorObserver, observer_list_,
                     OnCompositingShuttingDown(this));
 
   DCHECK(begin_frame_observer_list_.empty());
 
   if (root_layer_)
-    root_layer_->SetCompositor(NULL);
+    root_layer_->ResetCompositor();
 
   // Stop all outstanding draws before telling the ContextFactory to tear
   // down any contexts that the |host_| may rely upon.
   host_.reset();
 
   context_factory_->RemoveCompositor(this);
 }
 
 void Compositor::SetOutputSurface(
     scoped_ptr<cc::OutputSurface> output_surface) {
   host_->SetOutputSurface(output_surface.Pass());
 }
 
 void Compositor::ScheduleDraw() {
   host_->SetNeedsCommit();
 }
 
 void Compositor::SetRootLayer(Layer* root_layer) {
   if (root_layer_ == root_layer)
     return;
   if (root_layer_)
-    root_layer_->SetCompositor(NULL);
+    root_layer_->ResetCompositor();
   root_layer_ = root_layer;
-  if (root_layer_ && !root_layer_->GetCompositor())
-    root_layer_->SetCompositor(this);
   root_web_layer_->RemoveAllChildren();
   if (root_layer_)
-    root_web_layer_->AddChild(root_layer_->cc_layer());
+    root_layer_->SetCompositor(this, root_web_layer_);
 }
 
 void Compositor::SetHostHasTransparentBackground(
     bool host_has_transparent_background) {
   host_->set_has_transparent_background(host_has_transparent_background);
 }
 
 void Compositor::ScheduleFullRedraw() {
   // TODO(enne): Some callers (mac) call this function expecting that it
   // will also commit.  This should probably just redraw the screen
@@ skipping 220 matching lines @@
                     observer_list_,
                     OnCompositingLockStateChanged(this));
 }
 
 void Compositor::CancelCompositorLock() {
   if (compositor_lock_)
     compositor_lock_->CancelLock();
 }
 
 }  // namespace ui