Activate LayerImpl tree with sync+push instead of pointer swap

cc/tree_synchronizer_unittest.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/tree_synchronizer.h"
 
 #include <algorithm>
 
 #include "cc/layer.h"
 #include "cc/layer_animation_controller.h"
@@ skipping 125 matching lines @@
 
 protected:
     FakeImplProxy m_proxy;
     FakeLayerTreeHostImpl m_hostImpl;
 };
 
 // Attempts to synchronizes a null tree. This should not crash, and should
 // return a null tree.
 TEST_F(TreeSynchronizerTest, syncNullTree)
 {
-    scoped_ptr<LayerImpl> layerImplTreeRoot = TreeSynchronizer::synchronizeTrees(0, scoped_ptr<LayerImpl>(), m_hostImpl.activeTree());
+    scoped_ptr<LayerImpl> layerImplTreeRoot = TreeSynchronizer::synchronizeTrees(static_cast<Layer*>(NULL), scoped_ptr<LayerImpl>(), m_hostImpl.activeTree());
 
     EXPECT_TRUE(!layerImplTreeRoot.get());
 }
 
 // Constructs a very simple tree and synchronizes it without trying to reuse any preexisting layers.
 TEST_F(TreeSynchronizerTest, syncSimpleTreeFromEmpty)
 {
     scoped_refptr<Layer> layerTreeRoot = Layer::create();
     layerTreeRoot->addChild(Layer::create());
     layerTreeRoot->addChild(Layer::create());
@@ skipping 237 matching lines @@
 
     scoped_ptr<LayerImpl> layerImplTreeRoot = TreeSynchronizer::synchronizeTrees(layerTreeRoot.get(), scoped_ptr<LayerImpl>(), m_hostImpl.activeTree());
     TreeSynchronizer::pushProperties(layerTreeRoot.get(), layerImplTreeRoot.get());
     layerImplTreeRoot = TreeSynchronizer::synchronizeTrees(layerTreeRoot.get(), layerImplTreeRoot.Pass(), m_hostImpl.activeTree());
 
     EXPECT_TRUE(static_cast<FakeLayerAnimationController*>(layerTreeRoot->layerAnimationController())->synchronizedAnimations());
 }
 
 }  // namespace
 }  // namespace cc