Because the fake clock is getting out of sync with the real clock for the nonce flood tests, add a call to TestSleep::SyncFakeClock() in Clock::GetCurrentTime() to force a sync. Merged from http://go/wvgerrit/133223 Test: duration_use_case_test and nonce flood tests on bonito Bug: 198329759 Change-Id: Idfd92c6cc57750a52477189461220c682b302082