Remove usage of FakeRendererScheduler that's not necessary.

In some tests, FakeRendererScheduler is used to obtain the IPC task
runner. However, FakeRendererScheduler::IPCTaskRunner() just returns
nullptr, and there's no real point in using FakeRendererScheduler in
those tests.

This CL removes those unnecessary FakeRendererSchedulers, and passes
nullptr to the arguments where an IPC task runner is expected.

This CL is part of the refactoring of WebThreadScheduler.

Bug: 826203
Change-Id: Ie6800829b3f30cf19a1c2212e58e4cab505df80b
Reviewed-on: https://chromium-review.googlesource.com/c/1319224
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606367}
4 files changed