When changing from Tagged to Float64 representation, it's not unlikely
to see a HeapNumber (or if feedback says so, an Oddball), so we
shouldn't penalize the code that deals with this case by marking it as
deferred.

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

Review-Url: https://codereview.chromium.org/2295933003
Cr-Commit-Position: refs/heads/master@{#39025}