Fix gn bootstrap

BUG=803324
R=dpranke

Change-Id: Ib8a66495b9657da130a6608e6dacf6cf471cd504
Reviewed-on: https://chromium-review.googlesource.com/874870
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#530236}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 4c76252228505ce85f2965f71facaf41407f13c4