Implement pin storage backend.

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 4895538e928ab4157e0ae6109e8126f27288bae5..d77ee9ebf2ff9675ea1624102dde116a413cc451 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -868,6 +868,10 @@ const char kAllowScreenLock[] = "allow_screen_lock";
 // An int64 pref. This is a timestamp of the most recent time the profile took
 // or dismissed HaTS (happiness-tracking) survey.
 const char kHatsLastInteractionTimestamp[] = "hats_last_interaction_timestamp";
+
+// The salt and hash for the pin quick unlock mechanism.
+const char kQuickUnlockPinSalt[] = "quick_unlock.pin.salt";
+const char kQuickUnlockPinSecret[] = "quick_unlock.pin.secret";
 #endif  // defined(OS_CHROMEOS)
 
 // A boolean pref set to true if a Home button to open the Home pages should be