Add new BrowserForceSigninEnabeld policy option with future:true flag.

chrome/browser/policy/configuration_policy_handler_list_factory.cc

Index: chrome/browser/policy/configuration_policy_handler_list_factory.cc
diff --git a/chrome/browser/policy/configuration_policy_handler_list_factory.cc b/chrome/browser/policy/configuration_policy_handler_list_factory.cc
index a5bdd33addc3c914ef3b8749c63f3dd4729508db..bc3a703e3073ba81d7e2185e2c388b7dba8c0be9 100644
--- a/chrome/browser/policy/configuration_policy_handler_list_factory.cc
+++ b/chrome/browser/policy/configuration_policy_handler_list_factory.cc
@@ -573,6 +573,9 @@ const PolicyToPreferenceMapEntry kSimplePolicyMap[] = {
   { key::kBrowserAddPersonEnabled,
     prefs::kBrowserAddPersonEnabled,
     base::Value::TYPE_BOOLEAN },
+  { key::kForceBrowserSignin,
+    prefs::kForceBrowserSignin,
+    base::Value::TYPE_BOOLEAN },
 #endif  // !defined(OS_CHROMEOS) && !defined(OS_ANDROID)
 
 #if defined(OS_WIN)