Add a very basic PIN UI implementation that is shared between lock and settings.

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
index 185e94d87d64cfaae3edaabdbb16bbd9429bf9b0..180c9c15499df42280f462ac9298f2339fbb4db3 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -463,6 +463,8 @@ void SigninScreenHandler::DeclareLocalizedValues(
 
 void SigninScreenHandler::RegisterMessages() {
   AddCallback("authenticateUser", &SigninScreenHandler::HandleAuthenticateUser);
+  AddCallback("authenticateUserWithPin",
+              &SigninScreenHandler::HandleAuthenticateUserWithPin);
   AddCallback("launchIncognito", &SigninScreenHandler::HandleLaunchIncognito);
   AddCallback("showSupervisedUserCreationScreen",
               &SigninScreenHandler::HandleShowSupervisedUserCreationScreen);
@@ -1003,6 +1005,18 @@ void SigninScreenHandler::HandleAuthenticateUser(const AccountId& account_id,
   delegate_->Login(user_context, SigninSpecifics());
 }
 
+void SigninScreenHandler::HandleAuthenticateUserWithPin(
+    const AccountId& account_id, const std::string& password) {
+  if (!delegate_)
+    return;
+  DCHECK_EQ(account_id.GetUserEmail(),
+            gaia::SanitizeEmail(account_id.GetUserEmail()));
+
+  // TODO(jdufault): Implement this once the PIN authentication backend is in
+  // place.
+  LOG(ERROR) << "Implement SigninScreenHandler::HandleAuthenticateUserWithPin";

[xiyuan, 2016/05/02 20:03:33]

nit: We have NOTIMPLEMENTED() for this purpose.

[jdufault, 2016/05/03 19:21:58]

Done.

+}
+
 void SigninScreenHandler::HandleLaunchIncognito() {
   UserContext context(user_manager::USER_TYPE_GUEST, EmptyAccountId());
   if (delegate_)