Reland "Backport some tests in /remoting to SingleThreadTaskEnvironment"

This reverts commit 85d4a0fa5ae2afcd3d6c578a1465a23d74eb334a.

Reason for revert: most likely wrong culprit?

Original change's description:
> Revert "Backport some tests in /remoting to SingleThreadTaskEnvironment"
> 
> This reverts commit afa2cbc718a5063e2d797c30a63935b1e35bcfaf.
> 
> Reason for revert: non_viz_browser_tests failed because of:
> OAuth2Test.SetInvalidTokenStatus
> 
> https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-google-rel/6325
> 
> Original change's description:
> > Backport some tests in /remoting to SingleThreadTaskEnvironment
> > 
> > These tests were previously migrated from single-threaded MessageLoop to
> > a multi-threaded TaskEnvironment (then named ScopedTaskEnvironment) as
> > part of crbug.com/891670.
> > 
> > //base OWNERS decided in retrospect that it was better to keep a
> > single-threaded option for TaskEnvironment and introduced
> > SingleThreadTaskEnvironment. This CL retrofits that decision for
> > /remoting.
> > 
> > This CL is a no-op if it passes CQ.
> > 
> > This CL was uploaded by git cl split.
> > 
> > R=​[email protected]
> > 
> > Bug: 891670
> > Change-Id: Id50cc3412d6fbec3e5c71672bf74f6abf0f7332d
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786679
> > Auto-Submit: Gabriel Charette <[email protected]>
> > Reviewed-by: Lambros Lambrou <[email protected]>
> > Commit-Queue: Lambros Lambrou <[email protected]>
> > Cr-Commit-Position: refs/heads/master@{#693548}
> 
> [email protected],[email protected],[email protected]
> 
> Change-Id: Ibe96ffa6ddf39371dc64c6ad7236ec366f9331c4
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 891670
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787279
> Reviewed-by: Olga Sharonova <[email protected]>
> Commit-Queue: Olga Sharonova <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#693613}

[email protected],[email protected],[email protected],[email protected]

Change-Id: Idb489a187fcfb8343079c83f66088c6b6c8b5091
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 891670
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787184
Reviewed-by: Gabriel Charette <[email protected]>
Commit-Queue: Gabriel Charette <[email protected]>
Cr-Commit-Position: refs/heads/master@{#693829}
66 files changed