UMA for pin unlock success/failure.

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 10bfe44c76e23f9319811f26439e9e9f946bcc2c..823c9eb5bafb33ce003412a4feeab61cc2c332b4 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -1059,7 +1059,8 @@ void SigninScreenHandler::UpdateAddButtonStatus() {
 }
 
 void SigninScreenHandler::HandleAuthenticateUser(const AccountId& account_id,
-                                                 const std::string& password) {
+                                                 const std::string& password,
+                                                 bool authenticated_by_pin) {
   if (!delegate_)
     return;
   DCHECK_EQ(account_id.GetUserEmail(),
@@ -1067,6 +1068,7 @@ void SigninScreenHandler::HandleAuthenticateUser(const AccountId& account_id,
 
   UserContext user_context(account_id);

[jdufault, 2016/08/08 18:54:26]

I don't think we need to pass authenticated_by_pin since
IsPinAuthenticationAvailable should always equal it. But maybe pass it and add a
DCHECK with

  chromeos::PinStorage* pin_storage =
    chromeos::PinStorageFactory::GetForAccountId(user);
  DCHECK(pin_storage ||
         (authenticated_by_pin ==
           pin_storage->IsPinAuthenticationAvailable()));

[sammiequon, 2016/08/09 00:31:25]

Done.

   user_context.SetKey(Key(password));
+  user_context.SetIsUsingPin(authenticated_by_pin);
   delegate_->Login(user_context, SigninSpecifics());
 
   HidePinKeyboardIfNeeded(account_id);