Fix another bug in the gn_roll script.

We were not checking out the branch used to build gn before
checking on the tryjob statuses for that branch.

R=brettw@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1380373002

Cr-Original-Commit-Position: refs/heads/master@{#352145}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3862a3e5baf3e0e5c867d82df6615414ae914855
1 file changed
tree: cbac4b54d0be7804271b8618a76841da35f1ed9d
  1. tools/