Use ThreadScheduler::Current() in bindings/.

This CL replaces the occurrences of "Platform::Current()
->CurrentThread()->Scheduler()" with "ThreadScheduler::Current()"
which has the same meaning.

Also, this CL simplifies the code that assumes Thread::Scheduler()
can be null, which is no longer true.

Bug: 826203
Change-Id: I994db5b3be6e5e0f29cfe346dac15b49ca40394e
Reviewed-on: https://chromium-review.googlesource.com/c/1314079
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuta Kitamura <yutak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605271}
2 files changed