Introduce separate client and init path for single-threaded cc

ui/compositor/compositor.cc

 // Copyright (c) 2012 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 "ui/compositor/compositor.h"
 
 #include <algorithm>
 #include <deque>
 
 #include "base/bind.h"
@@ skipping 267 matching lines @@
       command_line->HasSwitch(cc::switches::kUIShowSurfaceDamageRects);
   settings.initial_debug_state.show_screen_space_rects =
       command_line->HasSwitch(cc::switches::kUIShowScreenSpaceRects);
   settings.initial_debug_state.show_replica_screen_space_rects =
       command_line->HasSwitch(cc::switches::kUIShowReplicaScreenSpaceRects);
   settings.initial_debug_state.show_occluding_rects =
       command_line->HasSwitch(cc::switches::kUIShowOccludingRects);
   settings.initial_debug_state.show_non_occluding_rects =
       command_line->HasSwitch(cc::switches::kUIShowNonOccludingRects);
 
-  scoped_refptr<base::SingleThreadTaskRunner> compositor_task_runner =
-      g_compositor_thread ? g_compositor_thread->message_loop_proxy() : NULL;
-
-  host_ =
-      cc::LayerTreeHost::Create(this, NULL, settings, compositor_task_runner);
+  if (!!g_compositor_thread) {
+    host_ = cc::LayerTreeHost::CreateThreaded(
+        this, NULL, settings, g_compositor_thread->message_loop_proxy());
+  } else {
+    host_ = cc::LayerTreeHost::CreateSingleThreaded(this, this, NULL, settings);
+  }
   host_->SetRootLayer(root_web_layer_);
   host_->SetLayerTreeHostClientReady();
 }
 
 Compositor::~Compositor() {
   TRACE_EVENT0("shutdown", "Compositor::destructor");
 
   DCHECK(g_compositor_initialized);
 
   CancelCompositorLock();
@@ skipping 247 matching lines @@
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingStarted(this, start_time));
 }
 
 void Compositor::DidCompleteSwapBuffers() {
   DCHECK(g_compositor_thread);
   NotifyEnd();
 }
 
+scoped_refptr<cc::ContextProvider> Compositor::OffscreenContextProvider() {
+  return ContextFactory::GetInstance()->OffscreenCompositorContextProvider();
+}
+
 void Compositor::ScheduleComposite() {
   if (!disable_schedule_composite_)
     ScheduleDraw();
 }
 
-scoped_refptr<cc::ContextProvider> Compositor::OffscreenContextProvider() {
-  return ContextFactory::GetInstance()->OffscreenCompositorContextProvider();
-}
-
 const cc::LayerTreeDebugState& Compositor::GetLayerTreeDebugState() const {
   return host_->debug_state();
 }
 
 void Compositor::SetLayerTreeDebugState(
     const cc::LayerTreeDebugState& debug_state) {
   host_->SetDebugState(debug_state);
 }
 
 scoped_refptr<CompositorLock> Compositor::GetCompositorLock() {
@@ skipping 34 matching lines @@
     // CompositorObservers to be notified before starting another
     // draw cycle.
     ScheduleDraw();
   }
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));
 }
 
 }  // namespace ui