Tolerate potentially dead methods in `Instrumentation`.

JIT GC can start while managed heap GC is running and
methods held by JIT are potentially dead.

Test: m test-art-host-gtest
Test: testrunner.py --host --jit
Change-Id: Ia5944fae5e375d18f0fe1a75df44005d8a6f97a3
4 files changed