Add a SigninAllowed policy.

chrome/browser/policy/configuration_policy_handler.cc

Index: chrome/browser/policy/configuration_policy_handler.cc
diff --git a/chrome/browser/policy/configuration_policy_handler.cc b/chrome/browser/policy/configuration_policy_handler.cc
index 5587cae14c2c6582bdbdd08633edf7282a5e7b15..ea01c560c001c090bffbf60c52fe1b7bc26b52c4 100644
--- a/chrome/browser/policy/configuration_policy_handler.cc
+++ b/chrome/browser/policy/configuration_policy_handler.cc
@@ -553,6 +553,23 @@ void SyncPolicyHandler::ApplyPolicySettings(const PolicyMap& policies,
     prefs->SetValue(prefs::kSyncManaged, value->DeepCopy());
 }
 
+// SigninPolicyHandler implementation ------------------------------------------
+
+SigninPolicyHandler::SigninPolicyHandler()
+    : TypeCheckingPolicyHandler(key::kSigninAllowed,
+                                Value::TYPE_BOOLEAN) {
+}
+
+SigninPolicyHandler::~SigninPolicyHandler() {
+}
+
+void SigninPolicyHandler::ApplyPolicySettings(const PolicyMap& policies,
+                                              PrefValueMap* prefs) {
+  const Value* value = policies.GetValue(policy_name());
+  bool signin_allowed;
+  if (value && value->GetAsBoolean(&signin_allowed))
+    prefs->SetValue(prefs::kSigninAllowed, value->DeepCopy());
+}
 
 // AutofillPolicyHandler implementation ----------------------------------------