cros: Add PinStorageProvider enum which describes pin backend in use.

chrome/browser/chromeos/login/quick_unlock/pin_storage_unittest.cc

Index: chrome/browser/chromeos/login/quick_unlock/pin_storage_unittest.cc
diff --git a/chrome/browser/chromeos/login/quick_unlock/pin_storage_unittest.cc b/chrome/browser/chromeos/login/quick_unlock/pin_storage_unittest.cc
index 039d6d5b190eafd0f7dac8e7ade916ac7ee8f9e4..bb7476b5e253af18fb34dc693582e265159ca74b 100644
--- a/chrome/browser/chromeos/login/quick_unlock/pin_storage_unittest.cc
+++ b/chrome/browser/chromeos/login/quick_unlock/pin_storage_unittest.cc
@@ -21,7 +21,9 @@ class PinStorageUnitTest : public testing::Test {
   ~PinStorageUnitTest() override {}
 
   // testing::Test:
-  void SetUp() override { quick_unlock::EnableForTesting(); }
+  void SetUp() override {
+    quick_unlock::EnableForTesting(quick_unlock::PinStorageProvider::Prefs);
+  }
 
   content::TestBrowserThreadBundle thread_bundle_;
   std::unique_ptr<TestingProfile> profile_;