cc : Fix bug in tree synchronization when mask layer changes

cc/layers/layer.cc

 // Copyright 2010 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.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 395 matching lines @@
 void Layer::SetMaskLayer(Layer* mask_layer) {
   DCHECK(IsPropertyChangeAllowed());
   if (mask_layer_.get() == mask_layer)
     return;
   if (mask_layer_.get()) {
     DCHECK_EQ(this, mask_layer_->parent());
     mask_layer_->RemoveFromParent();
   }
   mask_layer_ = mask_layer;
   if (mask_layer_.get()) {
+    mask_layer_->RemoveFromParent();
     DCHECK(!mask_layer_->parent());
-    mask_layer_->RemoveFromParent();
     mask_layer_->SetParent(this);
     mask_layer_->SetIsMask(true);
   }
   SetSubtreePropertyChanged();
   SetNeedsFullTreeSync();
 }
 
 void Layer::SetReplicaLayer(Layer* layer) {
   DCHECK(IsPropertyChangeAllowed());
   if (replica_layer_.get() == layer)
@@ skipping 1414 matching lines @@
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 gfx::Transform Layer::screen_space_transform() const {
   DCHECK_NE(transform_tree_index_, -1);
   return draw_property_utils::ScreenSpaceTransform(
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 }  // namespace cc