Fix race on mojo message pump shutdown.

mojo/message_pump/handle_watcher.cc

 // Copyright 2013 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 "mojo/message_pump/handle_watcher.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
@@ skipping 257 matching lines @@
 
 void WatcherThreadManager::AddRequest(const RequestData& data) {
   {
     base::AutoLock auto_lock(lock_);
     const bool was_empty = requests_.empty();
     requests_.push_back(data);
     if (!was_empty)
       return;
   }
 
-  // With the new Mojo EDK, the MojoMessagePump will destruct when it sees that
-  // the IO thread has gone away. So at shutdown this can be null.
-  if (!thread_.task_runner())
-    return;
-
   // We outlive |thread_|, so it's safe to use Unretained() here.
   thread_.task_runner()->PostTask(
       FROM_HERE,
       base::Bind(&WatcherThreadManager::ProcessRequestsOnBackendThread,
                  base::Unretained(this)));
 }
 
 void WatcherThreadManager::ProcessRequestsOnBackendThread() {
   DCHECK_EQ(thread_.message_loop(), base::MessageLoop::current());
 
@@ skipping 189 matching lines @@
         this, handle, handle_signals, deadline, callback));
   }
 }
 
 void HandleWatcher::Stop() {
   state_.reset();
 }
 
 }  // namespace common
 }  // namespace mojo