Start delegating notifications to MessageCenter on Windows.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index bc86059a0e120670429be4e43ce22be551425c63..4cb18fc8e94da7a771078e34e8452b0e18e71d73 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -64,6 +64,10 @@ class WindowModalityController;
 }
 }
 
+namespace message_center {
+class MessageCenter;
+}
+
 namespace ash {
 
 class AcceleratorController;
@@ -429,11 +433,14 @@ class ASH_EXPORT Shell
   }
 #endif  // defined(OS_CHROMEOS)
 
- aura::client::StackingClient* stacking_client();
+  aura::client::StackingClient* stacking_client();
 
- RootWindowHostFactory* root_window_host_factory() {
-   return root_window_host_factory_.get();
- }
+  RootWindowHostFactory* root_window_host_factory() {
+    return root_window_host_factory_.get();
+  }
+
+  // MessageCenter is a global list of currently displayed notifications.
+  message_center::MessageCenter* message_center();
 
  private:
   FRIEND_TEST_ALL_PREFIXES(ExtendedDesktopTest, TestCursor);
@@ -577,6 +584,8 @@ class ASH_EXPORT Shell
   scoped_ptr<internal::DisplayChangeObserverX11> display_change_observer_;
 #endif  // defined(OS_CHROMEOS)
 
+  scoped_ptr<message_center::MessageCenter> message_center_;
+
   CursorManager cursor_manager_;
 
   ObserverList<ShellObserver> observers_;