HandleScopeImplementer (since it isn't something specific to a
particular thread executing on an Isolate). This patch ensures correct
traversal of the handles when when multiple compilations are queued
up.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10778036

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12134 ce2b1a6d-e550-0410-aec6-3dcde31c8c00