Make sure key::kEnableWebBasedSignin policy also turns on command line arg

chrome/browser/policy/chrome_browser_policy_connector.cc

Index: chrome/browser/policy/chrome_browser_policy_connector.cc
diff --git a/chrome/browser/policy/chrome_browser_policy_connector.cc b/chrome/browser/policy/chrome_browser_policy_connector.cc
index e39d0109b4e24c1f16602062e3bd7edb2fb98f8e..49d70b19fee12fa74b80493bf4d2fe297c6698b3 100644
--- a/chrome/browser/policy/chrome_browser_policy_connector.cc
+++ b/chrome/browser/policy/chrome_browser_policy_connector.cc
@@ -133,7 +133,10 @@ void ChromeBrowserPolicyConnector::AppendExtraFlagPerPolicy() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   if (policy_value && policy_value->GetAsBoolean(&enabled) && enabled &&
       !command_line->HasSwitch(switches::kEnableWebBasedSignin)) {
+    // In M41, to fully enable web-based sign in, the kEnableIframeBasedSignin
+    // must also be specified.
     command_line->AppendSwitch(switches::kEnableWebBasedSignin);
+    command_line->AppendSwitch(switches::kEnableIframeBasedSignin);
   }
 }