Fix transaction bookkeeping for field CAS operations.

Record the old value only if the CAS is successful to avoid
"restoring" an old value that wasn't there during rollback.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I6459b680c216c0b9f7ac67f7b53f79ad37b39b80
3 files changed