Reboot test: Initialize fake clock

[ Merge of http://go/wvgerrit/143630 ]

When we run a test with the fake clock, the clock had been initialized
to the current time, or to 0. This causes a problem for reboot tests
because the clock might go backwards over the reboot. With this
change, we monitor the clock at the end of one reboot pass and
initialize the clock for the next pass based on the previous value.

Bug: 26163469
Test: GtsMediaTestCases on sunfish
Change-Id: Ibd0024f963634382af70553fced38da6e1d857d2

libwvdrmengine/cdm/util/test/test_sleep.h

@@ -41,6 +41,10 @@ class TestSleep {
   // verify this function does not roll back the clock used by OEMCrypto.
   static bool RollbackSystemTime(int seconds);
 
+  // Set the system clock to the specified time. This is only expected to work
+  // when real_sleep is false.
+  static void SetFakeClock(int64_t time_seconds);
+
   // Roll the system clock forward to undo all previous calls to
   // RollBackSystemTime. Returns true on success.
   static bool ResetRollback() {