Implement ping_freshness for update_client.

components/update_client/persisted_data_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 <string>
 #include <vector>
 
 #include "components/prefs/testing_pref_service.h"
 #include "components/update_client/persisted_data.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace update_client {
 
 TEST(PersistedDataTest, Simple) {
   std::unique_ptr<TestingPrefServiceSimple> pref(
       new TestingPrefServiceSimple());
   PersistedData::RegisterPrefs(pref->registry());
   std::unique_ptr<PersistedData> metadata(new PersistedData(pref.get()));
   EXPECT_EQ(-2, metadata->GetDateLastRollCall("someappid"));
   std::vector<std::string> items;
   items.push_back("someappid");
   metadata->SetDateLastRollCall(items, 3383);
   EXPECT_EQ(3383, metadata->GetDateLastRollCall("someappid"));
   EXPECT_EQ(-2, metadata->GetDateLastRollCall("someotherappid"));
+  const std::string pf1 = metadata->GetPingFreshness("someappid");
+  EXPECT_FALSE(pf1.empty());
   metadata->SetDateLastRollCall(items, 3386);
   EXPECT_EQ(3386, metadata->GetDateLastRollCall("someappid"));
   EXPECT_EQ(-2, metadata->GetDateLastRollCall("someotherappid"));
+  const std::string pf2 = metadata->GetPingFreshness("someappid");
+  EXPECT_FALSE(pf2.empty());
+  // The following has a 1 / 2^128 chance of being flaky.
+  EXPECT_NE(pf1, pf2);
 }
 
 TEST(PersistedDataTest, SharedPref) {
   std::unique_ptr<TestingPrefServiceSimple> pref(
       new TestingPrefServiceSimple());
   PersistedData::RegisterPrefs(pref->registry());
   std::unique_ptr<PersistedData> metadata(new PersistedData(pref.get()));
   EXPECT_EQ(-2, metadata->GetDateLastRollCall("someappid"));
   std::vector<std::string> items;
   items.push_back("someappid");
   metadata->SetDateLastRollCall(items, 3383);
 
   // Now, create a new PersistedData reading from the same path, verify
   // that it loads the value.
   metadata.reset(new PersistedData(pref.get()));
   EXPECT_EQ(3383, metadata->GetDateLastRollCall("someappid"));
   EXPECT_EQ(-2, metadata->GetDateLastRollCall("someotherappid"));
 }
 
 }  // namespace update_client