Revert of [scheduler] Add a CHECK for renderer main thread load metrics. (patchset #2 id:20001 of https://codereview.chromium.org/2720023003/ )

Reason for revert:
Revert temporary CHECK back to DCHECK

Original issue's description:
> [scheduler] Add a CHECK for renderer main thread load metrics.
>
> Change DCHECK to CHECK in RendererScheduler's
> Report{Foreground,Background}RendererThreadLoad. This should help pin
> down strange anomalies from metrics.
>
> This patch should be Canary-channel only, and expected to be extremely
> rare (less than 1 failure/day on Canary). Please revert without asking
> if something goes wrong.
>
> BUG=693542
>
> Review-Url: https://codereview.chromium.org/2720023003
> Cr-Commit-Position: refs/heads/master@{#453783}
> Committed: https://chromium.googlesource.com/chromium/src/+/2100af86f06ded92e913c67723bbff9af08df307

TBR=skyostil@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=693542

Review-Url: https://codereview.chromium.org/2769133003
Cr-Commit-Position: refs/heads/master@{#459088}
1 file changed