Transfer LayerImpl ownership to LayerTreeImpl

cc/test/fake_layer_tree_host.cc

Index: cc/test/fake_layer_tree_host.cc
diff --git a/cc/test/fake_layer_tree_host.cc b/cc/test/fake_layer_tree_host.cc
index cef4b32ea1c114d30299c1e2339ba4a21c526c53..e6fd914189b8d2b57c4441fa651bb4b5a892276b 100644
--- a/cc/test/fake_layer_tree_host.cc
+++ b/cc/test/fake_layer_tree_host.cc
@@ -81,14 +81,10 @@ const RendererCapabilities& FakeLayerTreeHost::GetRendererCapabilities() const {
 void FakeLayerTreeHost::SetNeedsCommit() { needs_commit_ = true; }
 
 LayerImpl* FakeLayerTreeHost::CommitAndCreateLayerImplTree() {
-  scoped_ptr<LayerImpl> old_root_layer_impl = active_tree()->DetachLayerTree();
-
-  scoped_ptr<LayerImpl> layer_impl = TreeSynchronizer::SynchronizeTrees(
-      root_layer(), std::move(old_root_layer_impl), active_tree());
+  TreeSynchronizer::SynchronizeTrees(root_layer(), active_tree());
+  LayerImpl* layer_impl = active_tree()->root_layer();
   active_tree()->SetPropertyTrees(*property_trees());
-  TreeSynchronizer::PushProperties(root_layer(), layer_impl.get());
-
-  active_tree()->SetRootLayer(std::move(layer_impl));
+  TreeSynchronizer::PushProperties(root_layer(), layer_impl);
   active_tree()->UpdatePropertyTreeScrollOffset(property_trees());
 
   if (page_scale_layer() && inner_viewport_scroll_layer()) {
@@ -105,14 +101,11 @@ LayerImpl* FakeLayerTreeHost::CommitAndCreateLayerImplTree() {
 }
 
 LayerImpl* FakeLayerTreeHost::CommitAndCreatePendingTree() {
-  scoped_ptr<LayerImpl> old_root_layer_impl = pending_tree()->DetachLayerTree();
-
-  scoped_ptr<LayerImpl> layer_impl = TreeSynchronizer::SynchronizeTrees(
-      root_layer(), std::move(old_root_layer_impl), pending_tree());
+  TreeSynchronizer::SynchronizeTrees(root_layer(), pending_tree());
+  LayerImpl* layer_impl = pending_tree()->root_layer();
   pending_tree()->SetPropertyTrees(*property_trees());
-  TreeSynchronizer::PushProperties(root_layer(), layer_impl.get());
+  TreeSynchronizer::PushProperties(root_layer(), layer_impl);
 
-  pending_tree()->SetRootLayer(std::move(layer_impl));
   pending_tree()->UpdatePropertyTreeScrollOffset(property_trees());
   return pending_tree()->root_layer();
 }