Fix gn bootstrap

R=dpranke

Change-Id: I880c2cc2a2702db6ebbbd90120753587971bb2be
Reviewed-on: https://chromium-review.googlesource.com/1067581
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#560326}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3685d34110d27fa6264a58bfb8c21e1880d07ad2