Adding implementation for MessageCenter::Delegate on MessageCeneterNotificationManager.

chrome/chrome_tests.gypi

Index: chrome/chrome_tests.gypi
diff --git a/chrome/chrome_tests.gypi b/chrome/chrome_tests.gypi
index 2b9d0e59fbe13bac3032bf53d944672395644e6d..7dae214d194001fea00a766386cacf5c5535e0bf 100644
--- a/chrome/chrome_tests.gypi
+++ b/chrome/chrome_tests.gypi
@@ -1186,6 +1186,7 @@
         'browser/net/predictor_browsertest.cc',
         'browser/net/proxy_browsertest.cc',
         'browser/net/websocket_browsertest.cc',
+        'browser/notifications/message_center_notifications_browsertest.cc',
         'browser/page_cycler/page_cycler_browsertest.cc',
         'browser/performance_monitor/performance_monitor_browsertest.cc',
         'browser/policy/cloud_policy_browsertest.cc',
@@ -1720,6 +1721,11 @@
             ['exclude', '^browser/ui/app_list/'],
           ],
         }],
+        ['enable_message_center==0 or use_ash==1', {
+          'sources!': [
+            'browser/notifications/message_center_notifications_browsertest.cc',
+          ],
+        }],
       ],  # conditions
     },  # target browser_tests
     {