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..728f3e944c5a7d2d94f98a0b11184735d1deef1b 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -1059,14 +1059,20 @@ 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(),
             gaia::SanitizeEmail(account_id.GetUserEmail()));
+  chromeos::PinStorage* pin_storage =
+    chromeos::PinStorageFactory::GetForAccountId(account_id);
+  DCHECK(pin_storage);
+  DCHECK(authenticated_by_pin == pin_storage->IsPinAuthenticationAvailable());

[jdufault, 2016/08/16 17:55:02]

Will authenticated_by_pin be true if the user types their password using the
virtual keyboard when the PIN keyboard is not shown?

If not, we should change this to

  DCHECK(pin_storage->IsPinAuthenticationAvailable() || !authenticated_by_pin)

Ie, if pin storage is not available, authenticated by PIN must be false. I'd add
a comment as well since that DCHECK is non-trivial to read.

Sorry for so many iterations here.

[sammiequon, 2016/08/16 19:22:11]

Done. Authenticated by pin will be true if the pin-keyboard was visible.

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