Use nanoTime() in finalizer watchdog

We want to stop the clock if the processor is powered down.

Bug: 156968512
Test: art/test/testrunner/testrunner.py --host -b --64
Change-Id: Ib615851fea78df1568305b8bcf8d9bea405a8f35
(cherry picked from commit 7809156fe25b5c8aa210f61fe1234a30a27e59bb)
1 file changed