Microbenchmarks show 25% improvement over C++, 11% improvement over JS
for the constructor. We don't have a microbenchmark covering the compile
method.

Locally, octane/regexp improved by 2%.

BUG=v8:5339

Review-Url: https://codereview.chromium.org/2551443002
Cr-Commit-Position: refs/heads/master@{#41490}