Partial revert of change to make Notification Center focusable after alt+shift+n

ui/message_center/views/message_center_view.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/message_center/views/message_center_view.h"
 
 #include <list>
 #include <map>
 
 #include "base/macros.h"
@@ skipping 510 matching lines @@
 
   if (is_locked_)
     SetVisibilityMode(Mode::BUTTONS_ONLY, animate);
   else if (settings_visible_)
     SetVisibilityMode(Mode::SETTINGS, animate);
   else if (no_message_views)
     SetVisibilityMode(Mode::BUTTONS_ONLY, animate);
   else
     SetVisibilityMode(Mode::NOTIFICATIONS, animate);
 
+  if (no_message_views) {
+    scroller_->SetFocusBehavior(FocusBehavior::NEVER);

[David Tseng, 2016/08/12 18:11:05]

Future note to xiyuan@
making this
+    scroller_->SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
does nothing with ChromeVox on.

+  } else {
+#if defined(OS_MACOSX)
+    scroller_->SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
+#else
+    scroller_->SetFocusBehavior(FocusBehavior::ALWAYS);
+#endif
+  }
+
   UpdateButtonBarStatus();
 
   if (focus_manager && focused_view)
     focus_manager->SetFocusedView(focused_view);
 
   if (scroller_->visible())
     scroller_->InvalidateLayout();
   PreferredSizeChanged();
   Layout();
 }
@@ skipping 82 matching lines @@
     // Disable the close-all button since no notification is visible.
     button_bar_->SetCloseAllButtonEnabled(false);
   }
 }
 
 void MessageCenterView::SetNotificationViewForTest(MessageView* view) {
   message_list_view_->AddNotificationAt(view, 0);
 }
 
 }  // namespace message_center