Adds the contextMessage field to notifications.

ui/message_center/cocoa/popup_collection_unittest.mm

 // Copyright (c) 2013 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.
 
 #import "ui/message_center/cocoa/popup_collection.h"
 
 #include "base/mac/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
@@ skipping 58 matching lines @@
     center_->AddNotification(notification.Pass());
 
     notification.reset(new message_center::Notification(
         message_center::NOTIFICATION_TYPE_SIMPLE,
         "3",
         ASCIIToUTF16("Three"),
         ASCIIToUTF16("This is the third notification "
                      "that has a much longer body "
                      "than the other notifications. It "
                      "may not fit on the screen if we "
-                     "set the screen size too small."),
+                     "set the screen size too small or "
+                     "if the notification is way too big"),
         gfx::Image(),
         string16(),
         message_center::NotifierId(),
         message_center::RichNotificationData(),
         NULL));
     center_->AddNotification(notification.Pass());
     WaitForAnimationEnded();
   }
 
   bool CheckSpacingBetween(MCPopupController* upper, MCPopupController* lower) {
@@ skipping 261 matching lines @@
       string16(),
       message_center::NotifierId(),
       message_center::RichNotificationData(),
       NULL));
   center_->UpdateNotification("1", notification.Pass());
 
   // Release the popup collection before the animation ends. No crash should
   // be expected.
   collection_.reset();
 }