Adds an ash global shortcut key for message center.

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index d1001f2f9ca854efc4707ac03299a2595916a1c8..de905dac2447dbf1ee2ef2a5f18b3c53bd567a28 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -33,6 +33,7 @@
 #include "ash/system/status_area_widget.h"
 #include "ash/system/tray/system_tray.h"
 #include "ash/system/tray/system_tray_delegate.h"
+#include "ash/system/web_notification/web_notification_tray.h"
 #include "ash/touch/touch_observer_hud.h"
 #include "ash/volume_control_delegate.h"
 #include "ash/wm/partial_screenshot_view.h"
@@ -631,6 +632,21 @@ bool AcceleratorController::PerformAction(int action,
         controller->GetSystemTray()->ShowDefaultView(BUBBLE_CREATE_NEW);
       break;
     }
+    case SHOW_MESSAGE_CENTER_BUBBLE: {
+      internal::RootWindowController* controller =
+          Shell::IsLauncherPerDisplayEnabled() ?
+          internal::RootWindowController::ForActiveRootWindow() :
+          Shell::GetPrimaryRootWindowController();
+      internal::StatusAreaWidget* status_area_widget =
+          controller->status_area_widget();
+      if (status_area_widget) {
+        WebNotificationTray* notification_tray =
+            status_area_widget->web_notification_tray();
+        if (notification_tray->visible())
+          notification_tray->ShowMessageCenterBubble();
+      }
+      break;
+    }
     case SHOW_TASK_MANAGER:
       Shell::GetInstance()->delegate()->ShowTaskManager();
       return true;