Const-ify RefCountedThreadSafe::AddRef and Release.

base/message_loop_proxy_impl.h

Index: base/message_loop_proxy_impl.h
diff --git a/base/message_loop_proxy_impl.h b/base/message_loop_proxy_impl.h
index b93bb64159203808ba70a5d081dc5ad4958aec9c..87ae70a7ff2c4d02c844ef7e9c0f2752c5f4c03a 100644
--- a/base/message_loop_proxy_impl.h
+++ b/base/message_loop_proxy_impl.h
@@ -39,7 +39,7 @@ class MessageLoopProxyImpl : public MessageLoopProxy,
  protected:
   // Override OnDestruct so that we can delete the object on the target message
   // loop if it still exists.
-  virtual void OnDestruct();
+  virtual void OnDestruct() const;
 
  private:
   MessageLoopProxyImpl();
@@ -50,7 +50,7 @@ class MessageLoopProxyImpl : public MessageLoopProxy,
   friend class MessageLoopProxy;
 
   // The lock that protects access to target_message_loop_.
-  Lock message_loop_lock_;
+  mutable Lock message_loop_lock_;
   MessageLoop* target_message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageLoopProxyImpl);