GN: Fix a memory leak found by LSAN.

Change-Id: I27d42d74889d455ac162c5701868fb5f2e837261
Reviewed-on: https://chromium-review.googlesource.com/885863
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#532183}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 31360b70f47bcc18df1501ed665793b693469f34