gn: Fix source paths Change-Id: Idf0c746d7e4e9f03b176744e8ff027be2d5f25ad Reviewed-on: https://chromium-review.googlesource.com/218520 Reviewed-by: Brett Wilson <brettw@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Commit-Queue: Cem Kocagil <ckocagil@chromium.org> Tested-by: Cem Kocagil <ckocagil@chromium.org>