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This is a reland of 63fbbb92

Reason for reland:
 - Fixed with ScopedAllowBaseSyncPrimitivesOutsideBlockingScope.

Original change's description:
> [ThreadPool]: Implement Job Delegate's ShouldYield and concurrency increase.
>
> This CL partially implement job's delegate, as well as concurrency
> usage assertion:
> - ShouldYield must be called in worker task.
> - max concurrency is expected to decrease unless
>   NotifyConcurrencyIncrease() is called.
>
> To implement ShouldYield, PooledTaskRunnerDelegate is used
> to communicate with ThreadPool and a racy priority is added to
> task source.
>
> Bug: 839091
> Change-Id: I3504f00ec48ab600f79b64e44151bc9dded408a8
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1713146
> Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
> Reviewed-by: François Doray <fdoray@chromium.org>
> Reviewed-by: Gabriel Charette <gab@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#690127}

Bug: 839091
Change-Id: I6f36f27426351e4efbcbaf7e9356840c004e6630
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769502
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690437}