cros: Add flag to enable pin on sign-in screen.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 4c3b8b21622dfcf73f9de4f48b297c597b9fc9da..adc6a233ea48a04cec7ac0ea6dcd4cf7da99cf1e 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2726,6 +2726,12 @@ const FeatureEntry kFeatureEntries[] = {
      flag_descriptions::kColorCorrectRenderingDescription, kOsAll,
      MULTI_VALUE_TYPE(kColorCorrectRenderingChoices)},
 
+#if defined(OS_CHROMEOS)
+    {"quick-unlock-pin-signin", flag_descriptions::kQuickUnlockPinSignin,
+     flag_descriptions::kQuickUnlockPinSigninDescription, kOsCrOS,
+     FEATURE_VALUE_TYPE(features::kQuickUnlockPinSignin)},
+#endif  // OS_CHROMEOS
+
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.