Update from https://crrev.com/317530

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 6dd0d5a74f7f00827868cc20be89f6dfe5bf7e57..60f4b4479f8814470a63215c6551217786158921 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -328,6 +328,8 @@ class CC_EXPORT LayerTreeHostImpl
   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();