Add GetIOMessageLoopProxy method to RenderThread interface.

content/test/mock_render_thread.cc

Index: content/test/mock_render_thread.cc
===================================================================
--- content/test/mock_render_thread.cc	(revision 137169)
+++ content/test/mock_render_thread.cc	(working copy)
@@ -71,6 +71,11 @@
   return NULL;
 }
 
+scoped_refptr<base::MessageLoopProxy>
+    MockRenderThread::GetIOMessageLoopProxy() {
+  return scoped_refptr<base::MessageLoopProxy>();
+}
+
 void MockRenderThread::AddRoute(int32 routing_id,
                                 IPC::Channel::Listener* listener) {
   // We may hear this for views created from OnMsgCreateWindow as well,