This reduces the number of times this string is copied from two to one.

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I8680cfc1ef1d6c2cfd3bc4970fe698bb904ce328
Reviewed-on: https://chromium-review.googlesource.com/652591Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47861}