This patch teaches Runtime.callFunctionOn to run evals inside its
task. This is aligned with how Runtime.evaluate works.

R=kozy

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I3189beebc9020703d2b2e23a7c828a2394d43910
Reviewed-on: https://chromium-review.googlesource.com/994070
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52339}