Re-land of http://codereview.chromium.org/6094009 with Mac build fix....

chrome/browser/gpu_process_host.h

Index: chrome/browser/gpu_process_host.h
===================================================================
--- chrome/browser/gpu_process_host.h	(revision 70681)
+++ chrome/browser/gpu_process_host.h	(working copy)
@@ -107,6 +107,11 @@
   void SendSynchronizationReply(IPC::Message* reply,
                                 RenderMessageFilter* filter);
 
+  // Sends outstanding replies to renderer processes. This is only called
+  // in error situations like the GPU process crashing -- but is necessary
+  // to prevent the renderer process from hanging.
+  void SendOutstandingReplies();
+
   virtual bool CanShutdown();
   virtual void OnChildDied();
   virtual void OnProcessCrashed(int exit_code);