[turbofan] Smartify the GraphReducer.

[turbofan] Smartify the GraphReducer.

Don't use the generic algorithm, but instead start going into the
direction of ControlReducer, using a stack plus a revisit queue to
not miss any more possibilities for reductions anymore.

TEST=cctest,unittests
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/726513002

Cr-Commit-Position: refs/heads/master@{#25326}