ChromeOS: Implement Network Selection screen of material design OOBE.

ui/webui/resources/js/polymer_config.js

 // Copyright 2015 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.
 
-if (typeof Polymer == 'undefined') {
-  Polymer = {
-    dom: 'shadow',
-    lazyRegister: true,
-    useNativeCSSProperties: true,
-  };
-} else {
-  console.error('Polymer is already defined.');
+var isChromePolymerInitialized;
+
+if (!isChromePolymerInitialized) {
+  isChromePolymerInitialized = true;

[stevenjb, 2016/07/07 16:58:41]

Make this change in a separate CL. Add dbeam@ and michaelpg@ as reviewers.

[Alexander Alekseev, 2016/07/08 01:12:29]

Done.

+  if (typeof Polymer == 'undefined') {
+    Polymer = {
+      dom: 'shadow',
+      lazyRegister: true,
+      useNativeCSSProperties: true,
+    };
+  } else {
+    console.error('Polymer is already defined.');
+  }
 }