The redundancy elimination is currently a graph reducer that tries to
combine redundant checks in the effect chain. It does this by
propagating the checks that happened along effect paths, which is pretty
similar to what the BranchElimination does on the control chain. We run
this reducer together with the other optimizations right after the
representation selection.

An upcoming CL will extend the redundancy elimination to also eliminate
redundant loads (and eventually map checks).

R=jarin@chromium.org
BUG=v8:5141

Review-Url: https://codereview.chromium.org/2091503003
Cr-Commit-Position: refs/heads/master@{#37208}