The change in question caused regressions on GC-heavy benchmarks,
presumably due to the added indirection that is taken within hot code
like the marking visitor.

This is a manual revert due to conflicts.

This reverts commit 4f55b830.

R=hpayer@chromium.org
BUG=chromium:539273
LOG=n

Review URL: https://codereview.chromium.org/1386863002

Cr-Commit-Position: refs/heads/master@{#31097}