Add missing include guard for notification_control_buttons_view.h

Bug: none
Change-Id: I48da5486779d4874a75d573b09c79b503925d992
Reviewed-on: https://chromium-review.googlesource.com/567900Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Commit-Queue: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485899}

ui/message_center/views/notification_control_buttons_view.h

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef UI_MESSAGE_CENTER_VIEWS_NOTIFICATION_CONTROL_BUTTONS_VIEW_H_
+#define UI_MESSAGE_CENTER_VIEWS_NOTIFICATION_CONTROL_BUTTONS_VIEW_H_
+
 #include "base/macros.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/animation/animation_delegate.h"
@@ -80,3 +83,5 @@ class MESSAGE_CENTER_EXPORT NotificationControlButtonsView
 };
 
 }  // namespace message_center
+
+#endif  // UI_MESSAGE_CENTER_VIEWS_NOTIFICATION_CONTROL_BUTTONS_VIEW_H_