Recognize a couple of builtins on the RegExp.prototype in the Typer and
assign useful types to them, so we can optimize various checks on their
results.

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

Review-Url: https://codereview.chromium.org/2531463002
Cr-Commit-Position: refs/heads/master@{#41240}