message: GuardDog test: NiceMock the MockSystemTimeSource.
  When this was changed from EXPECT_CALL to ON_CALL it introduced some
  unexpected mock warnings.  Use NiceMock.
diff: @@ -60,7 +60,7 @@ protected:
  NiceMock<Configuration::MockMain> config_kill_;
  NiceMock<Configuration::MockMain> config_multikill_;
  NiceMock<Stats::MockStore> fakestats_;
  - MockSystemTimeSource time_source_;
  + NiceMock<MockSystemTimeSource> time_source_;
  std::atomic<unsigned int> mock_time_;
  std::unique_ptr<GuardDogImpl> guard_dog_;
  WatchDogSharedPtr unpet_dog_;
  @@ -134,7 +134,7 @@ protected:
  NiceMock<Configuration::MockMain> config_miss_;
  NiceMock<Configuration::MockMain> config_mega_;
  Stats::IsolatedStoreImpl stats_store_;
  - MockSystemTimeSource time_source_;
  + NiceMock<MockSystemTimeSource> time_source_;
  std::atomic<unsigned int> mock_time_;
  };
  