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

chrome/browser/ui/sync/one_click_signin_helper.h

Index: chrome/browser/ui/sync/one_click_signin_helper.h
diff --git a/chrome/browser/ui/sync/one_click_signin_helper.h b/chrome/browser/ui/sync/one_click_signin_helper.h
index a2634d83fc2760a513abe32f417c53b4d953ffcc..773ab304ad33cc57d7c0fd10c639fc34ef50ebf2 100644
--- a/chrome/browser/ui/sync/one_click_signin_helper.h
+++ b/chrome/browser/ui/sync/one_click_signin_helper.h
@@ -97,6 +97,9 @@ class OneClickSigninHelper
                                     int child_id,
                                     int route_id);
 
+  // Returns true if a web-based sign in flow should be used.
+  static bool UseWebBasedSigninFlow();
+
  private:
   explicit OneClickSigninHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<OneClickSigninHelper>;