This CL introduces a new fast flat instantiations cache for the first 1024 object templates.
After that we fall back to the existing slower dictionary cache.

Drive-by-fix: de-handlify and clean up some code in api-natives.cc

BUG=chromium:630217

Review-Url: https://codereview.chromium.org/2170743003
Cr-Commit-Position: refs/heads/master@{#38146}