Remove {WebMain,}ThreadScheduler::{Add,Remove}PendingNavigation().

All overridden implementations of ThreadScheduler's interfaces are
no-op, so they can be removed without breaking any functionalities.

WebMainThreadScheduler's interfaces actually have some implementation.
However, they are not used by any production code, and only a few
tests depend on them.

There functions are perhaps the remnants of past refactoring. Since
nobody seems to rely on them currently, they can be removed entirely.

Bug: 826203
Change-Id: Ic8efe0afe09270c080bc7706287937a6da354ae1
Reviewed-on: https://chromium-review.googlesource.com/1055142
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558226}
14 files changed