Use WebCompositor only when --enable-threaded-compositing.

content/renderer/render_widget.cc

 // Copyright (c) 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 "content/renderer/render_widget.h"
 
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 907 matching lines @@
   // 2) Allows us to collect more damage rects before painting to help coalesce
   //    the work that we will need to do.
   invalidation_task_posted_ = true;
   MessageLoop::current()->PostTask(FROM_HERE, NewRunnableMethod(
       this, &RenderWidget::InvalidationCallback));
 }
 
 void RenderWidget::didActivateCompositor(int compositor_identifier) {
   TRACE_EVENT0("gpu", "RenderWidget::didActivateCompositor");
 
-  RenderThreadImpl::current()->compositor_thread()->
-      AddCompositor(routing_id_, compositor_identifier);
+  CompositorThread* compositor_thread =
+      RenderThreadImpl::current()->compositor_thread();
+  if (compositor_thread)

[jamesr, 2011/10/20 22:51:52]

in webkit we normally fold the assignment into the if() to scope the local. Do
we do this in chrome?

[darin (slow to review), 2011/10/21 05:03:35]

I don't think there is a strong convention.  It'd probably lead to some link
breaking here, which might be worse :)

+    compositor_thread->AddCompositor(routing_id_, compositor_identifier);
 
   is_accelerated_compositing_active_ = true;
   Send(new ViewHostMsg_DidActivateAcceleratedCompositing(
       routing_id_, is_accelerated_compositing_active_));
 
   // Note: asynchronous swapbuffer support currently only matters if
   // compositing scheduling happens on the RenderWidget.
   using_asynchronous_swapbuffers_ = SupportsAsynchronousSwapBuffers();
 }
 
@@ skipping 488 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }