Runtime.terminateExecution terminates current or next JavaScript
call. Termination flag is automatically reset as soon as v8 call
or microtasks are completed.

R=pfeldman@chromium.org

Bug: chromium:820640
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ie21c123be3a61fe25cf6e04c38a8b6c664622ed7
Reviewed-on: https://chromium-review.googlesource.com/957386
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51912}