Revert 176910 - Possible breakage of PlatformAppBrowserTest.Messaging

chrome/browser/resources/shared/css/bubble_button.css

Index: chrome/browser/resources/shared/css/bubble_button.css
===================================================================
--- chrome/browser/resources/shared/css/bubble_button.css	(revision 176923)
+++ chrome/browser/resources/shared/css/bubble_button.css	(working copy)
@@ -1,20 +0,0 @@
-/* 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.
- */
-
-.bubble-button {
-  display: inline-block;
-  height: 0;
-  line-height: 1;
-  vertical-align: middle;
-  width: 16px;
-}
-
-.bubble-button > div {
-  background-size: 16px;
-  height: 16px;
-  position: relative;
-  top: -8px;
-  width: 16px;
-}