Revert of Make document.rootScroller into an origin trial (patchset #3 id:40001 of https://codereview.chromium.org/2628923002/ )

Reason for revert:
Origin trial has been delayed for now

Original issue's description:
> Make document.rootScroller into an origin trial
>
> Intent-to-experiment:
> https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/COF0YKkjZVQ
>
> BUG=680190
>
> Review-Url: https://codereview.chromium.org/2628923002
> Cr-Commit-Position: refs/heads/master@{#443956}
> Committed: https://chromium.googlesource.com/chromium/src/+/f2b6b4c6b17f90d48d986c3856f4a422ddbdbc2c

TBR=iclelland@chromium.org,rbyers@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=680190

Review-Url: https://codereview.chromium.org/2707133008
Cr-Commit-Position: refs/heads/master@{#453905}
7 files changed