Fix 2x UI issues for Feedback.

ui/webui/resources/css/apps/common.css

 /* Copyright 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. */
 
 button.white-button,
 button.blue-button {
   border: 5px solid transparent;
   box-sizing: content-box;
   cursor: default;
   height: 21px;
@@ skipping 32 matching lines @@
 button.white-button[disabled] {
   border-image: -webkit-image-set(
     url('chrome://resources/images/apps/button_inactive.png') 1x,
     url('chrome://resources/images/2x/apps/button_inactive.png')
         2x) 5 fill / 5px / 2px repeat;
 }
 
 button.blue-button {
   border-image: -webkit-image-set(
     url('chrome://resources/images/apps/blue_button.png') 1x,
-    url('chrome://resources/images/2x/apps/_bluebutton.png')
+    url('chrome://resources/images/2x/apps/blue_button.png')
         2x) 5 fill / 5px / 2px repeat;
 }
 
 button.blue-button:hover {
   border-image: -webkit-image-set(
     url('chrome://resources/images/apps/blue_button_hover.png') 1x,
     url('chrome://resources/images/2x/apps/blue_button_hover.png')
         2x) 5 fill / 5px / 2px repeat;
 }
 
@@ skipping 30 matching lines @@
   background-image: -webkit-image-set(
     url('chrome://resources/images/apps/checkbox.png') 1x,
     url('chrome://resources/images/2x/apps/checkbox.png') 2x);
 }
 
 input[type='checkbox']:checked::after {
   background-image: -webkit-image-set(
     url('chrome://resources/images/apps/checkbox_checked.png') 1x,
     url('chrome://resources/images/2x/apps/checkbox_checked.png') 2x);
 }