Remove 'focusable' flag when there're no notifications.

ui/message_center/message_center_bubble.cc

 // Copyright (c) 2012 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/message_center_bubble.h"
 
 #include "grit/ui_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/size.h"
@@ skipping 192 matching lines @@
         break;
       }
     }
     if (num_children == 0) {
       views::Label* label = new views::Label(l10n_util::GetStringUTF16(
           IDS_MESSAGE_CENTER_NO_MESSAGES));
       label->SetFont(label->font().DeriveFont(1));
       label->SetEnabledColor(SK_ColorGRAY);
       scroll_content_->AddChildView(label);
       button_view_->SetCloseAllVisible(false);
+      scroller_->set_focusable(false);
     } else {
       button_view_->SetCloseAllVisible(true);
+      scroller_->set_focusable(true);
     }
     SizeScrollContent();
     Layout();
     if (GetWidget())
       GetWidget()->GetRootView()->SchedulePaint();
   }
 
   size_t NumMessageViews() const {
     return scroll_content_->child_count();
   }
@@ skipping 68 matching lines @@
 }
 
 void MessageCenterBubble::OnMouseExitedView() {
 }
 
 size_t MessageCenterBubble::NumMessageViewsForTest() const {
   return contents_view_->NumMessageViews();
 }
 
 }  // namespace message_center