Add DeadReferenceSafe annotation

Add a class annotation for selectively enabling dead reference
elimination. This should eventually become the default, but for
now it allows low-risk testing, and it allows us to enable this
selectively for classes where we think it may be especially beneficial.

The ART CL that actually looks at this is in progress.

Test: Tested with companion ART CL.

Bug: 111453875
Change-Id: I3ac4ce4ec253ee98841b12cea5f069e274fe069a
3 files changed