Implement ChildThread::shutdown and clear members that have refs into blink

content/child/child_thread.h

 // 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.
 
 #ifndef CONTENT_CHILD_CHILD_THREAD_H_
 #define CONTENT_CHILD_CHILD_THREAD_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory.h"
@@ skipping 32 matching lines @@
   // Creates the thread.
   ChildThread();
   // Used for single-process mode.
   explicit ChildThread(const std::string& channel_name);
   // ChildProcess::main_thread() is reset after Shutdown(), and before the
   // destructor, so any subsystem that relies on ChildProcess::main_thread()
   // must be terminated before Shutdown returns. In particular, if a subsystem
   // has a thread that post tasks to ChildProcess::main_thread(), that thread
   // should be joined in Shutdown().
   virtual ~ChildThread();
-  virtual void Shutdown() = 0;
+  virtual void Shutdown();
 
   // IPC::Sender implementation:
   virtual bool Send(IPC::Message* msg) OVERRIDE;
 
   // See documentation on MessageRouter for AddRoute and RemoveRoute
   void AddRoute(int32 routing_id, IPC::Listener* listener);
   void RemoveRoute(int32 routing_id);
 
   IPC::SyncChannel* channel() { return channel_.get(); }
 
@@ skipping 121 matching lines @@
   scoped_refptr<ChildResourceMessageFilter> resource_message_filter_;
 
   base::WeakPtrFactory<ChildThread> channel_connected_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ChildThread);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_CHILD_THREAD_H_