Recognize the special

  NumberFloor(NumberDivide(lhs, rhs))

subgraph in TypedOptimization, where both lhs and rhs are in the
Unsigned32 range, and the result is a PlainNumber, and replace the
NumberFloor with a NumberToUint32 truncation.

This could be done in a cleaner way if we have a dedicated type for all
double values in the Unsigned32 range, but that would complicate the
type system quite a bit.

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

Review-Url: https://codereview.chromium.org/2614663002
Cr-Commit-Position: refs/heads/master@{#42063}