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 2798fc4ec454fea268b8c4d874ab9537e9a94ce6..94df1ee67785e2e5317e8f2ac6a83bd5268e0e6a 100644
--- a/chrome/browser/chromeos/BUILD.gn
+++ b/chrome/browser/chromeos/BUILD.gn
@@ -800,8 +800,10 @@ 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",
@@ -1677,7 +1679,7 @@ 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",