Treat empty login_screen_input_methods policy as no-op

If an empty login_screen_input_methods policy is sent from the client,
treat it as if the policy was not present. Don't restrict input methods
in this case.

BUG=750572
TEST=browser_tests --gtest_filter=LoginScreenPolicyTest.*

Change-Id: I83109bb5c7648ac6a7f81da414879745bf905abb
Reviewed-on: https://chromium-review.googlesource.com/589436Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491380}

chrome/browser/chromeos/login/lock_screen_utils.cc

@@ -96,7 +96,9 @@ void EnforcePolicyInputMethods(std::string user_input_method) {
   chromeos::CrosSettings* cros_settings = chromeos::CrosSettings::Get();
   const base::ListValue* login_screen_input_methods = nullptr;
   if (!cros_settings->GetList(chromeos::kDeviceLoginScreenInputMethods,
-                              &login_screen_input_methods)) {
+                              &login_screen_input_methods) ||
+      login_screen_input_methods->empty()) {
+    StopEnforcingPolicyInputMethods();
     return;
   }
 

chrome/browser/chromeos/login/login_screen_policy_browsertest.cc

@@ -105,6 +105,29 @@ IN_PROC_BROWSER_TEST_F(LoginScreenPolicyTest, RestrictInputMethods) {
   ASSERT_EQ(0U, imm->GetActiveIMEState()->GetAllowedInputMethods().size());
 }
 
+IN_PROC_BROWSER_TEST_F(LoginScreenPolicyTest, PolicyInputMethodsListEmpty) {
+  content::WindowedNotificationObserver(
+      chrome::NOTIFICATION_LOGIN_OR_LOCK_WEBUI_VISIBLE,
+      content::NotificationService::AllSources())
+      .Wait();
+
+  input_method::InputMethodManager* imm =
+      input_method::InputMethodManager::Get();
+  ASSERT_TRUE(imm);
+
+  ASSERT_EQ(0U, imm->GetActiveIMEState()->GetAllowedInputMethods().size());
+
+  em::ChromeDeviceSettingsProto& proto(device_policy()->payload());
+  proto.mutable_login_screen_input_methods()->Clear();
+  EXPECT_TRUE(proto.has_login_screen_input_methods());
+  EXPECT_EQ(
+      0, proto.login_screen_input_methods().login_screen_input_methods_size());
+  RefreshDevicePolicyAndWaitForSettingChange(
+      chromeos::kDeviceLoginScreenInputMethods);
+
+  ASSERT_EQ(0U, imm->GetActiveIMEState()->GetAllowedInputMethods().size());
+}
+
 class LoginScreenLocalePolicyTest : public LoginScreenPolicyTest {
  protected:
   LoginScreenLocalePolicyTest() {}