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

chrome/common/extensions/api/identity_private.idl

+// Copyright (c) 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.
+
+namespace identityPrivate {
+
+  callback GetResourcesCallback = void (object result);
+
+  interface Functions {
+    // Gets resources required to render the API.
+    //
+    // |callback| : Called with a dictionary mapping names to resource strings.
+    static void getResources(GetResourcesCallback callback);
+  };
+
+  interface Events {
+    // Fired when a web flow dialog should be displayed.
+    static void onWebFlowRequest(DOMString key, DOMString url, DOMString mode);
+  };
+};