Eliminate invalid pointers in store buffer after marking.

Eliminate invalid pointers in store buffer after marking.

The store buffer can contain stale store buffer entries, i.e., slot in dead objects pointing to new space objects. These slots are treaded as live slots which cause problems with non-pointer fields and makes concurrent sweeping complicated. Removing these pointers from the store buffer before it is used makes life easier.

BUG=

Review URL: https://codereview.chromium.org/985453003

Cr-Commit-Position: refs/heads/master@{#27068}