Convert plugin and GPU process to brokered handle duplication.

content/browser/gpu/gpu_process_host.h

Index: content/browser/gpu/gpu_process_host.h
===================================================================
--- content/browser/gpu/gpu_process_host.h	(revision 132263)
+++ content/browser/gpu/gpu_process_host.h	(working copy)
@@ -41,7 +41,6 @@
   };
 
   typedef base::Callback<void(const IPC::ChannelHandle&,
-                              base::ProcessHandle,
                               const content::GPUInfo&)>
       EstablishChannelCallback;
 
@@ -165,9 +164,6 @@
   // Qeueud messages to send when the process launches.
   std::queue<IPC::Message*> queued_messages_;
 
-  // The handle for the GPU process or null if it is not known to be launched.
-  base::ProcessHandle gpu_process_;
-
   // Whether we are running a GPU thread inside the browser process instead
   // of a separate GPU process.
   bool in_process_;