CC Animations: Make LayerAnimationController creation optional

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 382 matching lines @@
 
 void Compositor::SetLayerTreeDebugState(
     const cc::LayerTreeDebugState& debug_state) {
   host_->SetDebugState(debug_state);
 }
 
 const cc::RendererSettings& Compositor::GetRendererSettings() const {
   return host_->settings().renderer_settings;
 }
 
+const cc::LayerTreeHost& Compositor::GetLayerTreeHost() const {
+  DCHECK(host_);
+  return *host_.get();
+}
+
 scoped_refptr<CompositorLock> Compositor::GetCompositorLock() {
   if (!compositor_lock_) {
     compositor_lock_ = new CompositorLock(this);
     host_->SetDeferCommits(true);
     FOR_EACH_OBSERVER(CompositorObserver,
                       observer_list_,
                       OnCompositingLockStateChanged(this));
   }
   return compositor_lock_;
 }
 
 void Compositor::UnlockCompositor() {
   DCHECK(compositor_lock_);
   compositor_lock_ = NULL;
   host_->SetDeferCommits(false);
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingLockStateChanged(this));
 }
 
 void Compositor::CancelCompositorLock() {
   if (compositor_lock_)
     compositor_lock_->CancelLock();
 }
 
 }  // namespace ui