cros: Implement cryptohome backend for pin.

chrome/browser/chromeos/BUILD.gn

Index: chrome/browser/chromeos/BUILD.gn
diff --git a/chrome/browser/chromeos/BUILD.gn b/chrome/browser/chromeos/BUILD.gn
index 0e1a8ff4976ccccc1dc5beb7ba9ac0e5052f6dc6..40364003e5ecddda0ba0c7b420242dbe58136e90 100644
--- a/chrome/browser/chromeos/BUILD.gn
+++ b/chrome/browser/chromeos/BUILD.gn
@@ -806,8 +806,10 @@ source_set("chromeos") {
     "login/proxy_settings_dialog.h",
     "login/quick_unlock/fingerprint_storage.cc",
     "login/quick_unlock/fingerprint_storage.h",
-    "login/quick_unlock/pin_storage.cc",
-    "login/quick_unlock/pin_storage.h",
+    "login/quick_unlock/pin_backend.cc",
+    "login/quick_unlock/pin_backend.h",
+    "login/quick_unlock/pin_storage_prefs.cc",
+    "login/quick_unlock/pin_storage_prefs.h",
     "login/quick_unlock/quick_unlock_factory.cc",
     "login/quick_unlock/quick_unlock_factory.h",
     "login/quick_unlock/quick_unlock_notification_controller.cc",
@@ -1694,7 +1696,7 @@ source_set("unit_tests") {
     "login/hwid_checker_unittest.cc",
     "login/profile_auth_data_unittest.cc",
     "login/quick_unlock/fingerprint_storage_unittest.cc",
-    "login/quick_unlock/pin_storage_unittest.cc",
+    "login/quick_unlock/pin_storage_prefs_unittest.cc",
     "login/quick_unlock/quick_unlock_storage_unittest.cc",
     "login/saml/saml_offline_signin_limiter_unittest.cc",
     "login/screens/network_screen_unittest.cc",