- we can avoid using regexps,
- this CL also fixed a bug.

R=alph@chromium.org

Bug: chromium:870957
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I9799507b85942be454a7c20d2768fe7442fc965e
Reviewed-on: https://chromium-review.googlesource.com/1250403
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56295}