During feedback typing (in SimplifiedLowering) we might be able to
constant-fold a bunch of ObjectIs<Type> predicates, i.e. because we
took type feedback on the input or we narrowed the type of a Phi
because of type feedback.

R=mvstanton@chromium.org
BUG=v8:5267,v8:5270

Review-Url: https://codereview.chromium.org/2342283002
Cr-Commit-Position: refs/heads/master@{#39468}