annotate: always prepare ancestry context of base fctx (
issue4600)
This patch extends the workaround introduced by
dd01834a696f. Even if the
base fctx is the same as intorrev, _ancestrycontext must be built for faster
_changeid lookup.
repo: https://hg.mozilla.org/releases/mozilla-beta
command: hg annotate -r
4954faa47dd0 gfx/thebes/gfxWindowsPlatform.cpp
before: 52.450 sec
after: 1.820 sec