branchmap: pass changelog into branchmap functions As part of building the branchmap, we loop over revs and call branchmap() or _branchmap(). Previously, these functions were accessing repo.changelog. We know from past experience that repo.changelog in loops is bad for performance. This commit teaches the branchmap code to pass a changelog instance into branchmap() and _branchmap() so we don't need to pay this penalty. On my MBP, this appears to show a speedup on a clone of the mozilla-unified repo: $ hg perfbranchmap --clear-revbranch ! base ! wall 21.078160 comb 21.070000 user 20.920000 sys 0.150000 (best of 3) ! wall 20.574682 comb 20.560000 user 20.400000 sys 0.160000 (best of 3) $ hg perfbranchmap ! base ! wall 4.880413 comb 4.870000 user 4.860000 sys 0.010000 (best of 3) ! wall 4.573968 comb 4.560000 user 4.550000 sys 0.010000 (best of 3) Differential Revision: https://phab.mercurial-scm.org/D5161