object space. Before, it was a link-list based look-up, and make this function
a little bit 'hot' from profile point.

BUG=v8:853
TEST=

Review URL: https://chromiumcodereview.appspot.com/9634005
Patch from Zhongping Wang <kewpie.w.zp@gmail.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11084 ce2b1a6d-e550-0410-aec6-3dcde31c8c00