[DevTools] Add "never show" link to emulation warning.

Source/devtools/front_end/responsiveDesignView.css

 /*
  * Copyright 2014 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.
  */
 
 .responsive-design {
     position: relative;
     background-color: rgb(0, 0, 0);
     overflow: hidden;
@@ skipping 421 matching lines @@
 .responsive-design-warning > span {
     flex: auto;
     padding-left: 3px;
     overflow: hidden;
 }
 
 .responsive-design-warning > div {
     flex: none;
 }
 
+.responsive-design-warning .disable-warning {
+    margin-right: 5px;
+    text-decoration: underline;
+    cursor: pointer;
+}
+
 .responsive-design-toggle-media-inspector .glyph {
     background-color: rgb(180, 180, 180);
     -webkit-mask-position: -128px -48px;
 }
 
 .responsive-design-toolbar button.responsive-design-toggle-media-inspector.toggled-on .glyph:not(.shadow) {
     background-color: rgb(105, 194, 236) !important;
 }
 
 /* Media query inspector */
@@ skipping 96 matching lines @@
     text-shadow: rgb(0, 0, 0) 1px 1px;
 }
 
 .media-inspector-label-right {
     right: 2px;
 }
 
 .media-inspector-label-left {
     left: 2px;
 }