Harmonize LayerTreeHost/LayerTreeHostImpl synchronization steps

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 05e54add9ff4d617bc0f5062f6bce38efc75ab54..72b69e0d7c66c8f9ca2655d461a6fe91ac7f6ad9 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -131,6 +131,17 @@ class CC_EXPORT LayerTreeImpl {
   void SetPropertyTrees(PropertyTrees* property_trees);
   PropertyTrees* property_trees() { return &property_trees_; }
 
+#if DCHECK_IS_ON()
+  // Returns true if the layer tree properties are safe to access. This occurs
+  // when the layer tree host is not currently syncing properties, or when a
+  // sync is in process but the property tree has been updated. See:
+  // |LayerTreeHostImpl::SyncState|.
+  bool PropertyTreeSyncComplete() const {
+    return layer_tree_host_impl_->SyncStateComplete(SYNCED_PROPERTY_TREES);

[enne (OOO), 2017/05/12 17:25:06]

Is it possible to just have this hidden inside of the property_trees()
LayerTreeImpl::property_trees accessor?

[pdr., 2017/05/15 18:30:24]

I've added a TODO comment here that we want to do this.

+  }
+#endif
+
+  void PushPropertyTreesTo(LayerTreeImpl* tree_impl);
   void PushPropertiesTo(LayerTreeImpl* tree_impl);
 
   void MoveChangeTrackingToLayers();