GitLab

This is a reland of 7a77c4e0

Death test should run in single thread. Adding
testing::GTEST_FLAG(death_test_style) = "threadsafe";
before EXPECT_DCHECK_DEATH() to fix flakiness.

Original change's description:
> [Task Scheduler]: Merge blocking and non-blocking pools.
>
> This CL creates a feature experiment that removes blocking worker pools
> from the task scheduler. Tasks with MayBlock trait are instead posted to
> the usual foreground/background pool, giving us better control over scheduling.
>
> Note: ScopedBlockingCall is used to add extra workers to the pool when a task is
> blocking. In this CL, we take advantage of this behavior to make sure enough
> workers are running on the CPU.
>
> Bug: 874080
> Change-Id: I7889a941f82203388c259b0d96073eb5ddf3de69
> Reviewed-on: https://chromium-review.googlesource.com/c/1249836
> Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
> Reviewed-by: François Doray <fdoray@chromium.org>
> Reviewed-by: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#600401}

TBR=rkaplow@chromium.org

Bug: 874080
Change-Id: I54665c798d332eead0f81da0f15c93368ec883a8
Reviewed-on: https://chromium-review.googlesource.com/c/1290911
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601122}