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

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/quick_unlock/quick_unlock_factory.h"
 #include "chrome/browser/chromeos/login/quick_unlock/quick_unlock_storage.h"
 #include "chrome/browser/chromeos/login/quick_unlock/quick_unlock_utils.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/testing_profile.h"
 #include "components/prefs/pref_service.h"
 #include "components/prefs/scoped_user_pref_update.h"
 #include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace chromeos {
 namespace {
 
 class PinStorageUnitTest : public testing::Test {
  protected:
   PinStorageUnitTest() : profile_(new TestingProfile()) {}
   ~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_;
 
   DISALLOW_COPY_AND_ASSIGN(PinStorageUnitTest);
 };
 
 }  // namespace
 
 // Provides test-only PinStorage APIs.
@@ skipping 96 matching lines @@
   EXPECT_TRUE(pin_storage_test.IsPinAuthenticationAvailable());
   for (int i = 0; i < quick_unlock::PinStorage::kMaximumUnlockAttempts; ++i)
     EXPECT_FALSE(pin_storage_test.TryAuthenticatePin("foobar"));
 
   // We used up all of the attempts, so entering the right PIN will still fail.
   EXPECT_FALSE(pin_storage_test.IsPinAuthenticationAvailable());
   EXPECT_FALSE(pin_storage_test.TryAuthenticatePin("1111"));
 }
 
 }  // namespace chromeos