fix gn bootstrap once again

BUG=None
TEST=./tools/gn/bootstrap/bootstrap.py
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/1455743002

Cr-Original-Commit-Position: refs/heads/master@{#360131}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5b67bfea1fea1bdcd3feb254d90c4147dee28f53
1 file changed
tree: f3d22aa7c4163bafc28240065816b69c86520b8a
  1. tools/