cc: Setup API to release OutputSurface from LTHClient.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index fa3ba0e599df1d93f2bbd0fdf3c7ce6f33c2a9cd..03441b7363ce474ef961ebdd87773e68ed1eecbe 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2155,10 +2155,7 @@ void LayerTreeHostImpl::CleanUpTileManager() {
   single_thread_synchronous_task_graph_runner_ = nullptr;
 }
 
-bool LayerTreeHostImpl::InitializeRenderer(
-    scoped_ptr<OutputSurface> output_surface) {
-  TRACE_EVENT0("cc", "LayerTreeHostImpl::InitializeRenderer");
-
+scoped_ptr<OutputSurface> LayerTreeHostImpl::ReleaseOutputSurface() {
   // Since we will create a new resource provider, we cannot continue to use
   // the old resources (i.e. render_surfaces and texture IDs). Clear them
   // before we destroy the old resource provider.
@@ -2168,8 +2165,15 @@ bool LayerTreeHostImpl::InitializeRenderer(
   renderer_ = nullptr;
   CleanUpTileManager();
   resource_provider_ = nullptr;
-  output_surface_ = nullptr;
 
+  return output_surface_.Pass();
+}
+
+bool LayerTreeHostImpl::InitializeRenderer(
+    scoped_ptr<OutputSurface> output_surface) {
+  TRACE_EVENT0("cc", "LayerTreeHostImpl::InitializeRenderer");
+
+  ReleaseOutputSurface();
   if (!output_surface->BindToClient(this)) {
     // Avoid recreating tree resources because we might not have enough
     // information to do this yet (eg. we don't have a TileManager at this