This will reduce heavy ScopeIterator instantiations.
Once incorporated into chromium, will give 30% speed boost.

BUG=chromium:340285
LOG=Y
R=ulan@chromium.org, Yang, rossberg, ulan

Review URL: https://codereview.chromium.org/181063008

Patch from Andrey Adaykin <aandrey@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19717 ce2b1a6d-e550-0410-aec6-3dcde31c8c00