Add logging if klass pointer found to be null.

It is unclear why klass pointer is observed to be nullptr some times
during marking phase of full-heap collection. It is possible that some
race condition is leading to this. To confirm, this CL adds a sleep and
then crashes.

Test: test/testrunner/testrunner.py
Bug: 173676071
Change-Id: I48dbdd38bf8261b7661ec3299678101c9c31c79e
1 file changed