Revert of Enable multiprocess by default on desktop mojo_runner.

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 <map>
 
 #include "base/atomic_sequence_num.h"
 #include "base/bind.h"
@@ skipping 204 matching lines @@
   Requests requests_;
 
   DISALLOW_COPY_AND_ASSIGN(WatcherThreadManager);
 };
 
 WatcherThreadManager::~WatcherThreadManager() {
   thread_.Stop();
 }
 
 WatcherThreadManager* WatcherThreadManager::GetInstance() {
-  // We need to leak this because otherwise when the process dies, AtExitManager
-  // waits for destruction which waits till the handle watcher thread is joined.
-  // But that can't happen since the pump uses mojo message pipes to wake up the
-  // pump. Since mojo EDK has been shutdown already, this never completes.
-  return base::Singleton<WatcherThreadManager,
-                         base::LeakySingletonTraits<WatcherThreadManager>>::
-      get();
+  return base::Singleton<WatcherThreadManager>::get();
 }
 
 WatcherID WatcherThreadManager::StartWatching(
     const Handle& handle,
     MojoHandleSignals handle_signals,
     base::TimeTicks deadline,
     const base::Callback<void(MojoResult)>& callback) {
   RequestData request_data;
   request_data.type = REQUEST_START;
   request_data.start_data.id = watcher_id_generator_.GetNext();
@@ skipping 230 matching lines @@
         this, handle, handle_signals, deadline, callback));
   }
 }
 
 void HandleWatcher::Stop() {
   state_.reset();
 }
 
 }  // namespace common
 }  // namespace mojo