[cros] Add --stub-cros-settings option for testing.

chrome/browser/chromeos/cros_settings_provider.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_CHROMEOS_CROS_SETTINGS_PROVIDER_H_
 #define CHROME_BROWSER_CHROMEOS_CROS_SETTINGS_PROVIDER_H_
 
 #include <string>
 
 #include "base/callback.h"
 
 namespace base {
 class Value;
 }
 
 namespace chromeos {
 
 class CrosSettingsProvider {
  public:
-  virtual ~CrosSettingsProvider() {}
+  // The callback type that is called to notify the CrosSettings observers
+  // about a setting change.
+  typedef base::Callback<void(const std::string&)> NotifyObserversCallback;
+
+  // Creates a new provider instance. |notify_cb| will be used to notify
+  // about setting changes.
+  explicit CrosSettingsProvider(const NotifyObserversCallback& notify_cb);
+  virtual ~CrosSettingsProvider();
 
   // Sets |in_value| to given |path| in cros settings.
   void Set(const std::string& path, const base::Value& in_value);
 
   // Gets settings value of given |path| to |out_value|.
   virtual const base::Value* Get(const std::string& path) const = 0;
 
   // Starts a fetch from the trusted store for the value of |path| if not loaded
   // yet. It will call the |callback| function upon completion if a new fetch
   // was needed in which case the return value is false. Else it will return
   // true and won't call the |callback|.
   virtual bool GetTrusted(const std::string& path,
                           const base::Closure& callback) = 0;
 
   // Gets the namespace prefix provided by this provider.
   virtual bool HandlesSetting(const std::string& path) const = 0;
 
   // Reloads the caches if the provider has any.
   virtual void Reload() = 0;
 
+ protected:
+  // Notifies the observers about a setting change.
+  void NotifyObservers(const std::string& path);
+
  private:
   // Does the real job for Set().
   virtual void DoSet(const std::string& path,
                      const base::Value& in_value) = 0;
+
+  // Callback used to notify about setting changes.
+  NotifyObserversCallback notify_cb_;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_CROS_SETTINGS_PROVIDER_H_