Make MessageLoopProxy::current() usable on threads that don't have MessageLoop.

base/message_loop_proxy_impl.cc

 // 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.
 
 #include "base/message_loop_proxy_impl.h"
 
 #include "base/location.h"
 #include "base/threading/thread_restrictions.h"
 
 namespace base {
@@ skipping 39 matching lines @@
   // function.
   // http://crbug.com/63678
   base::ThreadRestrictions::ScopedAllowSingleton allow_singleton;
   AutoLock lock(message_loop_lock_);
   return (target_message_loop_ &&
           (MessageLoop::current() == target_message_loop_));
 }
 
 // MessageLoop::DestructionObserver implementation
 void MessageLoopProxyImpl::WillDestroyCurrentMessageLoop() {
+  Detach();
   AutoLock lock(message_loop_lock_);
   target_message_loop_ = NULL;
 }
 
 void MessageLoopProxyImpl::OnDestruct() const {
   // We shouldn't use MessageLoop::current() since it uses LazyInstance which
   // may be deleted by ~AtExitManager when a WorkerPool thread calls this
   // function.
   // http://crbug.com/63678
   base::ThreadRestrictions::ScopedAllowSingleton allow_singleton;
@@ skipping 31 matching lines @@
 
 scoped_refptr<MessageLoopProxy>
 MessageLoopProxy::current() {
   MessageLoop* cur_loop = MessageLoop::current();
   if (!cur_loop)
     return NULL;
   return cur_loop->message_loop_proxy();
 }
 
 }  // namespace base