Reland "Migrate blink::WorkerPool away from CrossThreadBind"

This is a reland of 76b9fd7a715f57cda0ae1acd6c9f54cb8b922c56

This is the same as the original CL that got reverted. Problem was that
this original CL got merged before its blocking CL ( -
the relation chain got broken when I rebased it.

It should be all fine now for a reland.

Original change's description:
> Migrate blink::WorkerPool away from CrossThreadBind
> ... in favor of CrossThreadBindOnce.
> BUG=963574
> Change-Id: Iae1e8bc453c6806dfb0ce6c021d0eee18578f93f
> Reviewed-on:
> Commit-Queue: Antonio Gomes <>
> Auto-Submit: Antonio Gomes <>
> Reviewed-by: Kentaro Hara <>
> Cr-Commit-Position: refs/heads/master@{#661429}

Bug: 963574
Change-Id: Icf4354a63de5dcc421cbc6f3b84137907ec62b06
Reviewed-by: Antonio Gomes <>
Commit-Queue: Antonio Gomes <>
Cr-Commit-Position: refs/heads/master@{#661480}
11 files changed