Identity API: Change WebAuthFlow to use <webview> instead of a normal browser pop-up.

chrome/browser/resources/identity_api_ui/identity_api_ui.js

+// 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.
+
+chrome.identityPrivate.onWebFlowRequest.addListener(
+    function showAuthDialog(key, url, mode) {
+  var options = {
+    frame: 'none',
+    id: key,
+    minWidth: 1024,
+    minHeight: 768,
+    hidden: true
+  };
+  chrome.app.window.create('scope_approval_dialog.html', options,
+                           initializeWebFlow);
+
+  function initializeWebFlow(win) {
+    win.contentWindow.addEventListener('load', function(event) {
+      var windowParam;
+      if (mode == 'interactive')
+        windowParam = win;
+      win.contentWindow.start(url, windowParam);
+    });
+  }
+});
+