Ensure the GC visits Obsolete Methods

We were previously not visiting obsolete methods during GCs. This
could lead to the use of stale pointers.

Bug: 36335999
Test: ./test/testrunner/testrunner.py --host --interp-ac --gcstress -j40

Change-Id: I2b5c7c75b29f9037204a860501fcdb78104b5e7a
8 files changed