garbage collections when receiving idle notifications. This allows
us to get rid of source code strings and generated code in the
heap that would otherwise be kept around in idle V8 instances.
Review URL: http://codereview.chromium.org/450007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3375 ce2b1a6d-e550-0410-aec6-3dcde31c8c00