Revert of Move throttling of background timers into the renderer scheduler (patchset #16 id:300001 of https://codereview.chromium.org/1441073006/ )

Reason for revert:
Oops I'd meant to upload one final patchset before committing.

Original issue's description:
> Move throttling of background timers into the renderer scheduler
>
> Not only does this simplify the code, it's more efficent since
> previously setting the timer alignment resulted in mass cancellation
> and reposting of timers.
>
> BUG=510398, 546953, 560402
>
> Committed: https://crrev.com/ec5adec0a9879a31866e98c65ddc7b506b9f49c3
> Cr-Commit-Position: refs/heads/master@{#361971}

TBR=jochen@chromium.org,skyostil@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=510398, 546953, 560402

Review URL: https://codereview.chromium.org/1477353002

Cr-Commit-Position: refs/heads/master@{#361972}
55 files changed