Revert of [heap] Always use the passed-in collector in CollectGarbage. (patchset #1 id:1 of https://codereview.chromium.org/2336943003/ )

Reason for revert:
Regresses jank and memory. Revert for offline analysis.

Original issue's description:
> [heap] Always use the passed-in collector in CollectGarbage.
>
> Do not overwrite a collector decision.
>
> BUG=
>
> Committed: https://crrev.com/c19abaddafb5ede5e0d5efbe608b7fc5d7c7fcd0
> Cr-Commit-Position: refs/heads/master@{#39585}

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

Review-Url: https://codereview.chromium.org/2369933004
Cr-Commit-Position: refs/heads/master@{#39770}