The ControlEquivalence cannot deal with new nodes inserted by the
Scheduler due to Node splitting. Rather when the ControlEquivalence
sees such a new Node, it'll likely crash on an out-of-bounds access.

This is a speculative fix to make the crash disappear, as there's no
100% reliable repro currently.

BUG=chromium:629398
TBR=jochen@chromium.org

Review-Url: https://codereview.chromium.org/2611603002
Cr-Commit-Position: refs/heads/master@{#42016}