[DevTools] Initial implementation of device modes.

Source/devtools/front_end/emulation/overrides.css

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 128 matching lines @@
 
 .overrides-device .overrides-device-model-section > span {
     padding: 0 10px 0 3px;
 }
 
 .overrides-device .overrides-device-model-section select {
     width: 244px;
     height: 20px;
 }
 
+.device-art .overrides-device .overrides-device-model-section select.device-select {
+    width: 180px;
+    margin-right: 6px;
+}
+
+.overrides-device .overrides-device-model-section .mode-select {
+    display: none;
+    width: 140px;
+}
+
+.overrides-device .overrides-device-model-section .mode-select.invisible {
+    visibility: hidden;
+}
+
+.device-art .overrides-device .overrides-device-model-section .mode-select {
+    display: initial;
+}
+
 /* Media tab */
 
 .overrides-media > label {
     margin-bottom: 4px;
 }
 
 /* Sensors tab */
 
 .overrides-sensors > label {
     margin-bottom: 10px;
@@ skipping 93 matching lines @@
 #overrides-reset-button,
 #overrides-disable-button {
     margin: 9px 0 0 17px;
     display: block;
     width: 60px;
 }
 
 .overrides-enable-button {
     margin: 4px !important;
 }