Fix GN auto-roller to handle results from buildbucket-initiated jobs.
Fix GN auto-roller to handle results from buildbucket-initiated jobs.

It looks like we can get returned a try job state value of -1 now
when the try jobs are run through buildbucket instead of rietveld,
so this change updates the status mapping accordingly.

R=brettw@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1336713002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#348266}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,Chilledheart/chromium