Transfer LayerImpl ownership to LayerTreeImpl

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index a39d8b66d4332642ef1e3a4845535a93689bbb0a..ced57c210f2055baf89202f87a6d31e8d4b15c96 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -371,10 +371,9 @@ void LayerTreeHost::FinishCommitOnImplThread(LayerTreeHostImpl* host_impl) {
 
   sync_tree->set_source_frame_number(source_frame_number());
 
-  if (needs_full_tree_sync_) {
-    sync_tree->SetRootLayer(TreeSynchronizer::SynchronizeTrees(
-        root_layer(), sync_tree->DetachLayerTree(), sync_tree));
-  }
+  if (needs_full_tree_sync_)
+    TreeSynchronizer::SynchronizeTrees(root_layer(), sync_tree);
+
   sync_tree->set_needs_full_tree_sync(needs_full_tree_sync_);
   needs_full_tree_sync_ = false;