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

ui/message_center/message_center.h

Index: ui/message_center/message_center.h
diff --git a/ui/message_center/message_center.h b/ui/message_center/message_center.h
index 1b6cbae33c1bf7b608db470873c2a3978511ac71..84beb3536d834b9870a6af84c8db23829318e93f 100644
--- a/ui/message_center/message_center.h
+++ b/ui/message_center/message_center.h
@@ -103,6 +103,10 @@ class MESSAGE_CENTER_EXPORT MessageCenter {
                                          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