Enable web-based sign in flow by default. Can use command line argument

chrome/browser/ui/webui/sync_promo/sync_promo_ui.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_UI_WEBUI_SYNC_PROMO_SYNC_PROMO_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_SYNC_PROMO_SYNC_PROMO_UI_H_
 
 #include "content/public/browser/web_ui_controller.h"
 
 class Profile;
@@ skipping 49 matching lines @@
   // Gets the next page URL from the query portion of the sync promo URL.
   static GURL GetNextPageURLForSyncPromoURL(const GURL& url);
 
   // Gets the source from the query portion of the sync promo URL.
   // The source identifies from where the sync promo was opened.
   static Source GetSourceForSyncPromoURL(const GURL& url);
 
   // Returns whether the given sync URL contains auto_close parameter.
   static bool GetAutoCloseForSyncPromoURL(const GURL& url);
 
+  // Returns true if chrome should use the web-based sign in flow, false if
+  // chrome should use the ClientLogin flow.  This function will return true
+  // only for platforms where |ENABLE_ONE_CLICK_SIGNIN| is defined.
+  static bool UseWebBasedSigninFlow();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SyncPromoUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SYNC_PROMO_SYNC_PROMO_UI_H_