cc : Fix bug in tree synchronization when mask layer changes

cc/layers/layer_impl.cc

 // Copyright 2012 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/layers/layer_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 131 matching lines @@
 }
 
 void LayerImpl::ClearChildList() {
   if (children_.empty())
     return;
   for (auto* child : children_)
     layer_tree_impl_->RemoveLayer(child->id());
   children_.clear();
 }
 
+void LayerImpl::ClearLinksToOtherLayers() {
+  children_.clear();
+  mask_layer_ = nullptr;
+  replica_layer_ = nullptr;
+}
+
 void LayerImpl::SetScrollParent(LayerImpl* parent) {
   if (scroll_parent_ == parent)
     return;
 
   if (parent)
     DCHECK_EQ(layer_tree_impl()->LayerById(parent->id()), parent);
 
   scroll_parent_ = parent;
   SetNeedsPushProperties();
 }
@@ skipping 1442 matching lines @@
            .layer_transforms_should_scale_layer_contents) {
     return default_scale;
   }
 
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
       DrawTransform(), default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }
 
 }  // namespace cc