The helper class in question is no longer needed now that frame states
representing the "before" state is not attached to nodes anymore. They
are represented by appropriate {Checkpoint} nodes in the graph now.

R=bmeurer@chromium.org
BUG=v8:5021

Review-Url: https://codereview.chromium.org/2205243002
Cr-Commit-Position: refs/heads/master@{#38288}