[turbofan] Narrow upper bounds during typed lowering.

[turbofan] Narrow upper bounds during typed lowering.

This is a temporary solution, which optionally narrows upper bounds of
nodes when changing the operator of a node.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/741503006

Cr-Commit-Position: refs/heads/master@{#25658}