+ little reduction of injected-script-source size.

Bug: chromium:759651
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ia5d0b31fddc9f6c6c7e547618a6a01e93564bcbc
Reviewed-on: https://chromium-review.googlesource.com/660409Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47958}