cc : Fix bug in tree synchronization when mask layer changes

cc/trees/tree_synchronizer.cc

 // 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.
 
 #include "cc/trees/tree_synchronizer.h"
 
 #include <stddef.h>
 
 #include <set>
 
@@ skipping 15 matching lines @@
   scoped_ptr<OwnedLayerImplList> old_layers(tree_impl->DetachLayers());
 
   OwnedLayerImplMap old_layer_map;
   for (auto& it : *old_layers)
     old_layer_map[it->id()] = std::move(it);
 
   SynchronizeTreesRecursive(&old_layer_map, layer_root, tree_impl);
 
   for (auto& it : old_layer_map) {
     if (it.second) {
-      // Need to ensure that layer destruction doesn't tear down child
-      // LayerImpl that have been used in the new tree.
-      it.second->children().clear();
+      // Need to ensure that layer destruction doesn't tear down other layers
+      // linked to this LayerImpl that have been used in the new tree.
+      it.second->ClearLinksToOtherLayers();
     }
   }
 }
 
 void TreeSynchronizer::SynchronizeTrees(Layer* layer_root,
                                         LayerTreeImpl* tree_impl) {
   if (!layer_root)
     tree_impl->ClearLayers();
   else
     SynchronizeTreesInternal(layer_root, tree_impl);
@@ skipping 150 matching lines @@
                               impl_tree);
 
 #if DCHECK_IS_ON()
   if (host_tree->root_layer() && impl_tree->root_layer())
     CheckScrollAndClipPointersRecursive(host_tree->root_layer(),
                                         impl_tree->root_layer());
 #endif
 }
 
 }  // namespace cc