StandardRepositories: Add OpenJDK 9+181.

This affects the behavior of the CompareUpstreams and CopyUpstreamFiles tools.
I haven't re-run those tools because they don't currently work for another
reason (I haven't managed to rebuild OpenJDK 8) but it should this change
should be correct.

CompareUpstreams.java's toplevel documentation already lists
instructions for how to check out OpenJDK 9+181.

This CL is a prerequisite for being able to refer to OpenJDK 9+181 as a
potential reference upstream for particular files.

I also renamed referenceUpstreamAsOfAndroidP() -> referenceUpstream(),
since the semantics of that method have changed over time rather than
being tied specifically to Android P.

Test: Nothing.
Bug: 129875045

Change-Id: I66b3768eb0ab807f2fe58fb7cfff4bee4d1e3583
3 files changed