ChromeOS OOBE: Implement network selection screen "Back" button.

chrome/browser/resources/chromeos/login/oobe_welcome.html

 <!-- Copyright 2016 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. -->
 
 <link rel="import" href="chrome://resources/cr_elements/network/cr_network_icon.html">
 <link rel="import" href="chrome://resources/cr_elements/network/cr_network_select.html">
 <link rel="import" href="chrome://resources/cr_elements/network/cr_onc_types.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-iconset-svg/iron-iconset-svg.html">
 
 <iron-iconset-svg name="oobe-welcome" size="24">
   <svg>
     <defs>
-      <g id="add"><path d="M19 13h-6v6h-2v-6H5v-2h6V5h2v6h6v2z"></path></g>
       <g id="wifi"><path d="M1 9l2 2c4.97-4.97 13.03-4.97 18 0l2-2C16.93 2.93 7.08 2.93 1 9zm8 8l3 3 3-3c-1.65-1.66-4.34-1.66-6 0zm-4-4l2 2c2.76-2.76 7.24-2.76 10 0l2-2C15.14 9.14 8.87 9.14 5 13z"></path></g>
     </defs>
   </svg>
 </iron-iconset-svg>
 
+<iron-iconset-svg name="oobe-welcome-20" size="20">
+  <svg>
+    <defs>
+      <g id="add-cellular" stroke="none" stroke-width="1" fill="none" fill-rule="evenodd">
+        <g transform="translate(1.000000, 0.000000)">

[michaelpg, 2016/11/14 21:25:19]

These icon definitions have a lot of extra junk: unnecessary transformations,
unused IDs, etc. Can you squash them? See
https://www.chromium.org/developers/updating-webui-for-material-design/using-...
for guidance.

[Alexander Alekseev, 2016/11/15 01:23:00]

Done.

+          <polygon id="Shape" points="0 0 18 0 18 18 0 18"></polygon>
+          <path d="M8.20703249,16 L1,16 L16,1 L16,9.59970959 C15.2499322,9.21627867 14.4002234,9 13.5,9 C10.4624339,9 8,11.4624339 8,14.5 C8,15.0200119 8.07216716,15.5231682 8.20703249,16 Z" id="Combined-Shape" fill-opacity="0.3" fill="#000000"></path>
+          <path d="M15,14 L15,11 L13,11 L13,14 L10,14 L10,16 L13,16 L13,19 L15,19 L15,16 L18,16 L18,14 L15,14 Z" id="Combined-Shape" fill="#000000"></path>
+        </g>
+      </g>
+      <g id="add-wifi" transform="translate(1.000000, 1.000000)">
+          <path d="M9.04381443,16.25 L0.5,5.26075269 C0.828608247,5.00483871 4.09278351,2.25 9,2.25 C13.8999141,2.25 17.1713918,5.00483871 17.5,5.26075269 L15.8095005,7.45764359 C15.3190107,7.3016991 14.7978835,7.21774194 14.257732,7.21774194 C11.3539668,7.21774194 9,9.64406974 9,12.6370968 C9,13.635184 9.26176768,14.5702526 9.71839927,15.3733424 L9.04381443,16.25 Z" id="Combined-Shape" fill-opacity="0.3"></path>
+          <path d="M16,12 L16,9 L14,9 L14,12 L11,12 L11,14 L14,14 L14,17 L16,17 L16,14 L19,14 L19,12 L16,12 Z" id="Combined-Shape"></path>
+      </g>
+      <g id="add-proxy" fill="#000000">
+        <g transform="translate(1.000000, 1.000000)">
+          <path d="M15,13 L15,10 L13,10 L13,13 L10,13 L10,15 L13,15 L13,18 L15,18 L15,15 L18,15 L18,13 L15,13 Z" id="Combined-Shape"></path>
+          <path d="M7.04,14.48 C6.30,14.38 5.61,14.15 4.98,13.82 C4.94,13.80 4.91,13.79 4.87,13.77 C4.79,13.72 4.71,13.67 4.63,13.62 C4.54,13.57 4.45,13.51 4.36,13.45 C4.30,13.41 4.25,13.37 4.19,13.32 C4.08,13.25 3.98,13.17 3.88,13.09 C3.83,13.05 3.79,13.01 3.74,12.97 C3.64,12.87 3.54,12.78 3.44,12.68 C3.40,12.64 3.36,12.60 3.32,12.56 C3.23,12.45 3.13,12.35 3.04,12.23 C3.00,12.19 2.97,12.15 2.94,12.11 C2.85,11.99 2.76,11.87 2.68,11.75 C2.65,11.71 2.62,11.66 2.59,11.62 C2.51,11.49 2.44,11.37 2.37,11.24 C2.34,11.19 2.31,11.14 2.29,11.09 C2.22,10.96 2.16,10.83 2.10,10.69 C2.08,10.64 2.05,10.59 2.03,10.53 C1.98,10.40 1.93,10.26 1.89,10.12 C1.87,10.07 1.85,10.01 1.83,9.95 C1.79,9.81 1.76,9.67 1.73,9.53 C1.71,9.47 1.69,9.40 1.68,9.34 C1.65,9.19 1.63,9.05 1.62,8.90 C1.61,8.84 1.60,8.78 1.59,8.72 C1.57,8.51 1.56,8.30 1.56,8.08 C1.56,7.58 1.62,7.11 1.72,6.64 L5.47,10.50 L5.47,11.31 C5.47,12.19 6.18,12.92 7.04,12.92 L7.04,14.48 Z M10.17,9.08 L10.17,8.89 C10.17,8.44 9.82,8.08 9.39,8.08 L4.69,8.08 L4.69,6.47 L6.26,6.47 C6.69,6.47 7.04,6.11 7.04,5.66 L7.04,4.05 L8.60,4.05 C9.46,4.05 10.17,3.32 10.17,2.44 L10.17,2.11 C12.23,2.97 13.74,4.93 14.03,7.27 L14.02,7.27 C14.02,7.31 14.03,7.34 14.03,7.37 C14.07,7.37 14.11,7.37 14.15,7.37 C14.66,7.37 15.15,7.44 15.62,7.58 C15.62,7.48 15.62,7.37 15.61,7.27 L15.61,7.27 C15.29,4.03 13.10,1.34 10.17,0.39 L10.17,0.39 C10.17,0.39 10.16,0.39 10.16,0.39 C10.13,0.38 10.10,0.37 10.08,0.36 C9.88,0.30 9.68,0.25 9.48,0.20 C9.41,0.19 9.34,0.18 9.28,0.16 C9.10,0.13 8.92,0.10 8.75,0.08 C8.68,0.07 8.61,0.06 8.55,0.06 C8.31,0.03 8.07,0.02 7.82,0.02 C3.50,0.02 0,3.63 0,8.08 C0,12.53 3.50,16.14 7.82,16.14 C8.33,16.14 8.82,16.09 9.30,16.00 C8.83,15.15 8.56,14.17 8.56,13.13 C8.56,11.55 9.17,10.12 10.17,9.08 L10.17,9.08 Z" id="Fill-2" fill-opacity="0.3"></path>
+        </g>
+      </g>
+    </defs>
+  </svg>
+</iron-iconset-svg>
+
 <dom-module name="oobe-welcome-md">
   <template>
     <link rel="stylesheet" href="oobe_dialog_host.css">
     <link rel="stylesheet" href="oobe_welcome.css">
     <link rel="stylesheet" href="oobe_dialog_parameters.css">
     <oobe-welcome-dialog id="welcomeScreen" hidden="[[!welcomeScreenShown]]"
         current-language="[[currentLanguage]]"
         on-language-button-clicked="onWelcomeSelectLanguageButtonClicked_"
         on-accessibility-button-clicked="onWelcomeAccessibilityButtonClicked_"
         on-next-button-clicked="onWelcomeNextButtonClicked_">
@@ skipping 87 matching lines @@
           <span class="unchecked-value" i18n-content="virtualKeyboardOptionOff">
           </span>
         </oobe-a11y-option>
       </div>
       <div class="bottom-buttons layout horizontal end-justified">
         <oobe-text-button inverse on-tap="closeAccessibilitySection_">
           <div i18n-content="oobeOKButtonText"></div>
         </oobe-text-button>
       </div>
     </oobe-dialog>
-    <oobe-dialog hidden="[[!networkSelectionScreenShown]]">
+    <oobe-dialog id="networkSelectionScreen"
+        hidden="[[!networkSelectionScreenShown]]" has-buttons>
       <iron-icon icon="oobe-welcome:wifi" class="oobe-icon"></iron-icon>
       <div class="header">
         <h1 class="title" i18n-content="networkSectionTitle"></h1>
         <div class="subtitle" i18n-content="networkSectionHint"></div>
       </div>
       <div class="footer layout vertical">
         <cr-network-select id="networkSelect"
             on-network-connected="onNetworkConnected_"
             on-network-item-selected="onNetworkListNetworkItemSelected_"
             on-custom-item-selected="onNetworkListCustomItemSelected_"
             custom-items="[[_getNetworkCustomItems()]]"
-            max-height="385">
+            max-height="307">
         </cr-network-select>
       </div>
+      <div class="bottom-buttons layout horizontal start-justified">
+        <oobe-back-button on-tap="onNetworkSelectionBackButtonPressed_">
+        </oobe-back-button>
+      </div>
     </oobe-dialog>
   </template>
 </dom-module>