Support notifications with custom content

ui/message_center/message_center.gyp

Index: ui/message_center/message_center.gyp
diff --git a/ui/message_center/message_center.gyp b/ui/message_center/message_center.gyp
index 3744eb7e62f0e3f799b9d278dcd5890c1984861e..5cb36b8e5b02821e6ad1fb989bf598a39068f7f3 100644
--- a/ui/message_center/message_center.gyp
+++ b/ui/message_center/message_center.gyp
@@ -60,6 +60,7 @@
         'notification_blocker.h',
         'notification_delegate.cc',
         'notification_delegate.h',
+        'notification_delegate_views.cc',
         'notification_list.cc',
         'notification_list.h',
         'notification_types.cc',
@@ -72,6 +73,8 @@
         'popup_timers_controller.h',
         'views/bounded_label.cc',
         'views/bounded_label.h',
+        "views/custom_notification_view.cc",
+        "views/custom_notification_view.h",
         'views/constants.h',
         'views/desktop_popup_alignment_delegate.cc',
         'views/desktop_popup_alignment_delegate.h',
@@ -90,6 +93,8 @@
         'views/message_popup_collection.h',
         'views/message_view.cc',
         'views/message_view.h',
+        'views/message_view_factory.cc',
+        'views/message_view_factory.h',
         'views/message_view_context_menu_controller.cc',
         'views/message_view_context_menu_controller.h',
         'views/notification_button.cc',
@@ -131,6 +136,7 @@
         }, {
           'sources/': [
             ['exclude', 'views/'],
+            ['exclude', '_views\\.(h|cc)$'],
           ],
         }],
         # iOS disables notifications altogether, Android implements its own
@@ -222,6 +228,7 @@
           ],
           'sources': [
             'views/bounded_label_unittest.cc',
+            'views/custom_notification_view_unittest.cc',
             'views/message_center_view_unittest.cc',
             'views/message_popup_collection_unittest.cc',
             'views/notification_view_unittest.cc',