Add reachabilityFence, ReachabilitySensitive

Add the @ReachabilitySensitive annotation itself, and use it
in libcore itself, where needed.

Import OpenJDK9+181's reachabilityFence, so that it can be used in
preference to the annotation where it makes sense. Java 9's
stopgap reachabilityFence implementation doesn't work for us,
so replace it with a different stopgap.

The libcore changes correct many situations in which finalizers
could previously run prematurely according to the JLS. Or they
would correct them if we had a real implementation for
@ReachabilitySensitive.

The ZipFile constructor could close the file before notifying the
CloseGuard that it was open.

Aside from the ZipFile change, there should be no functional
change, yet.

Note that the ExemptionMechanism.java fix is the same as upstream.

Conspicuously missing:

- Any code, e.g. in ART or D8, that actually looks for the annotation.
- Uses in frameworks code, where it's probably most critical.

Bug: 63934467
Bug: 70906684
Bug: 28342794
Test: Build & boot AOSP
Change-Id: I652f0625b39b2ba9ac901d4f63e6aa6cf3b74af5

0 files changed, 0 insertions, 0 deletions