Add a workaround for null klass during marking phase

There is a race condition due to which sometimes we read a null class
pointer from an object during marking phase in AddLiveBytesAndScanRef().
This CL adds a workaround (until the root cause is identified). The
workaround is to wait a small amount of time and read the class
pointer again, which seems to work.

Test: art/test/testrunner/testrunner.py
Bug: 173676071
Bug: 173771057
Change-Id: I96004341c54593e9e6c5b4fa4a2ec6713acd0af7
1 file changed