It is not safe to assume the first match is a string just
because the RegExp result is fast.

Bug: chromium:831943
Change-Id: Idd40f8b75312f0be54f45f626dc017339033abc6
Reviewed-on: https://chromium-review.googlesource.com/1009325Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Wong <peter.wm.wong@gmail.com>
Cr-Commit-Position: refs/heads/master@{#52578}