Adds a small icon to notifications, and connects it to synced notifications.

ui/message_center/message_center.h

 // 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.
 
 #ifndef UI_MESSAGE_CENTER_MESSAGE_CENTER_H_
 #define UI_MESSAGE_CENTER_MESSAGE_CENTER_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 85 matching lines @@
   // Sets the large image for the notifications of type == TYPE_IMAGE. Specified
   // image will appear below of the notification.
   virtual void SetNotificationImage(const std::string& notification_id,
                                     const gfx::Image& image) = 0;
 
   // Sets the image for the icon of the specific action button.
   virtual void SetNotificationButtonIcon(const std::string& notification_id,
                                          int button_index,
                                          const gfx::Image& image) = 0;
 
+  // Sets the small image for the notification.
+  virtual void SetNotificationSmallImage(const std::string& notification_id,

[Dmitry Titov, 2014/01/29 23:07:05]

If we don't call this and don't plan to in the near future, it's better not to
add the dead code. It is easy to add it when and if it'll be needed. Consider
removing this method.
Also, in FakeMessageCenter this method goes above SetNotificationButtonIcon()...

[dewittj, 2014/01/30 00:41:56]

Done.

+                                         const gfx::Image& image) = 0;
+
   // Operations happening especially from GUIs: click, expand, disable,
   // and settings.
   // Searches through the notifications and disables any that match the
   // extension id given.
   virtual void DisableNotificationsByNotifier(
       const NotifierId& notifier_id) = 0;
 
   // Reformat a notification to show its entire text content.
   virtual void ExpandNotification(const std::string& id) = 0;
 
@@ skipping 56 matching lines @@
   MessageCenter();
   virtual ~MessageCenter();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MessageCenter);
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_MESSAGE_CENTER_H_