Fix gn bootstrap

R=dpranke

Change-Id: I9f93686d2bab2d3625363142bb05349817e1c5b5
Reviewed-on: https://chromium-review.googlesource.com/982250
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#546160}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: c89b8fabf7a9234c9d073cad1e5931d10fa28a34