GitLab

Also use base::StringPiece rather than a std::string reference. It
avoids some unnecessary copies in the substrings.

Bug: 814591
Change-Id: I7a1a0387b09038f7e084b2baf7b67716c729710a
Reviewed-on: https://chromium-review.googlesource.com/953744Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541652}