Update from https://crrev.com/317530

cc/trees/layer_tree_host_impl.h

 // Copyright 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 310 matching lines @@
   void DidModifyTilePriorities();
 
   LayerTreeImpl* active_tree() { return active_tree_.get(); }
   const LayerTreeImpl* active_tree() const { return active_tree_.get(); }
   LayerTreeImpl* pending_tree() { return pending_tree_.get(); }
   const LayerTreeImpl* pending_tree() const { return pending_tree_.get(); }
   LayerTreeImpl* recycle_tree() { return recycle_tree_.get(); }
   const LayerTreeImpl* recycle_tree() const { return recycle_tree_.get(); }
   // Returns the tree LTH synchronizes with.
   LayerTreeImpl* sync_tree() {
+    // TODO(enne): This is bogus.  It should return based on the value of
+    // Proxy::CommitToActiveTree and not whether the pending tree exists.
     return pending_tree_ ? pending_tree_.get() : active_tree_.get();
   }
   virtual void CreatePendingTree();
   virtual void ActivateSyncTree();
 
   // Shortcuts to layers on the active tree.
   LayerImpl* RootLayer() const;
   LayerImpl* InnerViewportScrollLayer() const;
   LayerImpl* OuterViewportScrollLayer() const;
   LayerImpl* CurrentlyScrollingLayer() const;
@@ skipping 392 matching lines @@
   bool is_likely_to_require_a_draw_;
 
   scoped_ptr<FrameTimingTracker> frame_timing_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_