[RunLoop] Remove unused RunLoop::OverrideDelegateForCurrentThreadForTesting().

This is effectively a revert of r521228 while keeping the improvements
of r524097.

This was intended to be used to allow ScopedTaskEnvironment::MOCK_TIME
on top of MessageLoopForUI/ForIO but this turned out harder than
expected and we're now going with a different approach.

R=danakj@chromium.org

Bug: 708584
Change-Id: I6951ac7fc1bf6b6eac0f269e0dec9f677ea29543
Reviewed-on: https://chromium-review.googlesource.com/1066456
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560695}

CrOS-Libchrome-Original-Commit: 50518fc77cc0e960c20137a16406cd0d10056890
5 files changed
tree: 56a4988714da4cf8c1d2c5f8f3af6adf949a62f8
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/