Remove FetchContext::GetFrameScheduler

Remove FetchContext::GetFrameScheduler calls from
ResourceLoadScheduler.
 - AddLifecycleObserver is called at the construction time, so
   provide the frame scheduler via ResourceFetcherInit.
 - GetFrameStatus calls are replaced by
   ResourceFetcherProperties::GetFrameStatus.

ResourceLoadScheduler was the only user of
FetchContext::GetFrameScheduler, so we can remove it now.

Bug: 914739
Change-Id: I367cf96e06aadf7006b631a32fe3aa671fe69af9
Reviewed-on: https://chromium-review.googlesource.com/c/1402303
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627299}
18 files changed