This saves us 14.2kB binary size in libv8.so (in release mode), and
probably also improves performance a little bit.

R=titzer@chromium.org

Bug: v8:7109
Change-Id: I345a48369aaf054572a4fd4368bf5cd526ed146a
Reviewed-on: https://chromium-review.googlesource.com/797270Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49905}