High promotion mode limits new space size in the case where many objects (high
rate) are promoted.  The result is frequent scavenger runs with low pause times. The
approach conflicts with pretenuring which requires a larger new space size to
collect enough feedback to be usable.

Ultimately the goal is to have pretenuring catch allocation sites that have high
promotion rates.

Revert "Bring back high promotion mode to shrink young generation size when scavenging latency is high."

This reverts commit 37be1d5e.

Revert "GC. Delay/avoid entering high promotion mode"

This reverts commit a5221d07.

BUG=chromium:499507,chromium:506910
LOG=n

Review URL: https://codereview.chromium.org/1247723003

Cr-Commit-Position: refs/heads/master@{#29983}