MacViews: Implement Full Keyboard Access.

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 583 matching lines @@
       no_message_views ? empty_list_view_.get() : message_list_view_.get());
 
   bool no_closable_views = true;
   for (const auto& view : notification_views_) {
     if (!view.second->IsPinned()) {
       no_closable_views = false;
       break;
     }
   }
   button_bar_->SetCloseAllButtonEnabled(!no_closable_views);
-  scroller_->SetFocusBehavior(no_message_views ? FocusBehavior::NEVER
-                                               : FocusBehavior::ALWAYS);
+
+  if (no_message_views) {
+    scroller_->SetFocusBehavior(FocusBehavior::NEVER);
+  } else {
+#if defined(OS_MACOSX)
+    scroller_->SetFocusBehavior(FocusBehavior::ACCESSIBLE_ONLY);
+#else
+    scroller_->SetFocusBehavior(FocusBehavior::ALWAYS);
+#endif
+  }
 
   if (focus_manager && focused_view)
     focus_manager->SetFocusedView(focused_view);
 
   scroller_->InvalidateLayout();
   PreferredSizeChanged();
   Layout();
 }
 
 void MessageCenterView::SetNotificationViewForTest(MessageView* view) {
   message_list_view_->AddNotificationAt(view, 0);
 }
 
 }  // namespace message_center