Pausable Object cleanup - ScriptedTaskQueue

Remove usage of pausable object in the scripted task queue. The
experimental web scheduler queues that are created already are
frame specific pausable queues. Confirmed this with the author
of this code as this code was duplicated from the idle task runner which
isn't a frame specific queue.

BUG=907125

Change-Id: Ibb1aaff62c2a6f2b482a3a7a190cb71baeea3b6c
Reviewed-on: https://chromium-review.googlesource.com/c/1378237
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617130}
3 files changed