Re-enable Alt-Shift-N for UnifiedSystemTray.

Alt-Shift-N was disabled for UnifiedSystemTray. Because we have
Alt-Shift-S. https://crrev.com/c/1023500

In response to feedback, the expected behavior of Alt-Shift-N is
changed, and now it does the same action as Alt-Shift-S.

TEST=manual
BUG=none

Change-Id: I8314e8205512d70c095b7ca45839f386e7a8fea7
Reviewed-on: https://chromium-review.googlesource.com/1147780Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578961}

ash/accelerators/accelerator_controller.cc

@@ -413,7 +413,7 @@ void HandleTakeScreenshot() {
 
 bool CanHandleToggleMessageCenterBubble() {
   if (features::IsSystemTrayUnifiedEnabled())
-    return false;
+    return true;
   aura::Window* target_root = Shell::GetRootWindowForNewWindows();
   StatusAreaWidget* status_area_widget =
       Shelf::ForWindow(target_root)->shelf_widget()->status_area_widget();
@@ -421,24 +421,6 @@ bool CanHandleToggleMessageCenterBubble() {
          status_area_widget->notification_tray()->visible();
 }
 
-void HandleToggleMessageCenterBubble() {
-  base::RecordAction(UserMetricsAction("Accel_Toggle_Message_Center_Bubble"));
-  aura::Window* target_root = Shell::GetRootWindowForNewWindows();
-  StatusAreaWidget* status_area_widget =
-      Shelf::ForWindow(target_root)->shelf_widget()->status_area_widget();
-  if (!status_area_widget)
-    return;
-  NotificationTray* notification_tray = status_area_widget->notification_tray();
-  if (!notification_tray->visible())
-    return;
-  if (notification_tray->IsMessageCenterVisible()) {
-    notification_tray->CloseBubble();
-  } else {
-    notification_tray->ShowBubble(false /* show_by_click */);
-    notification_tray->ActivateBubble();
-  }
-}
-
 void HandleToggleSystemTrayBubble() {
   base::RecordAction(UserMetricsAction("Accel_Toggle_System_Tray_Bubble"));
   aura::Window* target_root = Shell::GetRootWindowForNewWindows();
@@ -464,6 +446,28 @@ void HandleToggleSystemTrayBubble() {
   }
 }
 
+void HandleToggleMessageCenterBubble() {
+  base::RecordAction(UserMetricsAction("Accel_Toggle_Message_Center_Bubble"));
+  if (features::IsSystemTrayUnifiedEnabled()) {
+    HandleToggleSystemTrayBubble();
+    return;
+  }
+  aura::Window* target_root = Shell::GetRootWindowForNewWindows();
+  StatusAreaWidget* status_area_widget =
+      Shelf::ForWindow(target_root)->shelf_widget()->status_area_widget();
+  if (!status_area_widget)
+    return;
+  NotificationTray* notification_tray = status_area_widget->notification_tray();
+  if (!notification_tray->visible())
+    return;
+  if (notification_tray->IsMessageCenterVisible()) {
+    notification_tray->CloseBubble();
+  } else {
+    notification_tray->ShowBubble(false /* show_by_click */);
+    notification_tray->ActivateBubble();
+  }
+}
+
 void HandleShowTaskManager() {
   base::RecordAction(UserMetricsAction("Accel_Show_Task_Manager"));
   Shell::Get()->new_window_controller()->ShowTaskManager();