This reverts commit bfc9eb2e.

Reason for revert: Micro-benchmark regressions (crbug.com/923823)

Original change's description:
> [scanner] Micro-optimize AdvanceUntil
> 
> Replace std::find_if in AdvanceUntil with a manual loop, which can
> then return early, skipping the branch comparing to buffer_end_.
> 
> Change-Id: If49ed3667877751fcb0103a742750f03e5bd50db
> Reviewed-on: https://chromium-review.googlesource.com/c/1411351
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#58846}

TBR=leszeks@chromium.org,verwaest@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.
Bug: 923823

Change-Id: I2475e18fb1d52d47b32b34e261c6f1aa46b3c1ce
Reviewed-on: https://chromium-review.googlesource.com/c/1425200Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58962}