[Mac] During shutdown, do not post NSApplicationWillTerminateNotification twice.

chrome/browser/lifetime/application_lifetime_mac.mm

 // 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.
 
+// This file contains the penultimate pieces of the Mac shutdown puzzle. For
+// an in-depth overview of the Mac shutdown path, see the comment above
+// -[BrowserCrApplication terminate:].
+
 #include "chrome/browser/lifetime/application_lifetime.h"
 
+#include "base/bind.h"
+#include "base/message_loop.h"
 #include "chrome/browser/browser_shutdown.h"
 #import "chrome/browser/chrome_browser_application_mac.h"
 
 namespace browser {
 
+namespace {
+
+// A closure that is used to finalize application shutdown.
+void PerformTerminate() {
+  [[NSNotificationCenter defaultCenter]
+      postNotificationName:NSApplicationWillTerminateNotification
+                    object:NSApp];
+}
+
+}  // namespace
+
+// At this point, the user is trying to quit (or the system is forcing the
+// application to quit) and all browsers have been successfully closed. The
+// final step in shutdown is to post the NSApplicationWillTerminateNotification
+// to end the -[NSApplication run] event loop. That is performed via the
+// MessageLoop, since this can be called via the destruction path of the last
+// Browser object.
 void HandleAppExitingForPlatform() {
-  // Last browser is closed, so call back to controller to shutdown the app.
-  chrome_browser_application_mac::Terminate();
+  static bool kill_me_now = false;
+  CHECK(!kill_me_now);
+  kill_me_now = true;
+
+  MessageLoop::current()->PostNonNestableTask(FROM_HERE,
+      base::Bind(&PerformTerminate));
 }
 
 }  // namespace browser