Create a ProfileDependencyManager to order ProfileKeyedService destruction.

chrome/browser/profiles/profile_keyed_service.h

+// Copyright (c) 2011 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.
+
+#ifndef CHROME_BROWSER_PROFILES_PROFILE_KEYED_SERVICE_H_
+#define CHROME_BROWSER_PROFILES_PROFILE_KEYED_SERVICE_H_
+
+// Base class for all ProfileKeyedServices to allow for correct destruction
+// order.
+//
+// Many services that hang off Profile have a two-pass shutdown. Many
+// subsystems need a first pass shutdown phase where they drop references. Not
+// all services will need this, so there's a default implementation. Only once
+// every system has been given a chance to drop references do we start deleting
+// objects.
+class ProfileKeyedService {
+ public:
+  // The first pass is to call Shutdown on a ProfileKeyedService.
+  virtual void Shutdown() {}
+
+  // The second pass is the actual deletion of each object.
+  virtual ~ProfileKeyedService() {}
+};
+
+#endif  // CHROME_BROWSER_PROFILES_PROFILE_KEYED_SERVICE_H_
+