cc : Fix bug in tree synchronization when mask layer changes

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index bcbec39c4b8cfabad04d0dfd3002c6c6ce3f305b..5688e4ee347544504ebc270fa5e714f1c8c84801 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -149,6 +149,12 @@ void LayerImpl::ClearChildList() {
   children_.clear();
 }
 
+void LayerImpl::ClearLinksToOtherLayers() {
+  children_.clear();
+  mask_layer_ = nullptr;
+  replica_layer_ = nullptr;
+}
+
 void LayerImpl::SetScrollParent(LayerImpl* parent) {
   if (scroll_parent_ == parent)
     return;