This shows around a 2.2x speedup compared to the old JS implementation (and
3.5x compared to CPP) for the fast path.

Adds ToUint32 to CodeStubAssembler.

BUG=v8:5339

Review-Url: https://codereview.chromium.org/2532403002
Cr-Commit-Position: refs/heads/master@{#41408}