Do not unnecessarily expose execution state in debug event data.

When we fire a debug event, we create duplicate execution state objects,
one as argument for the debug event listener, one as property on the
debug event data object. The latter is never used by chrome.

R=yurys@chromium.org

Review URL: https://codereview.chromium.org/355793002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22001 ce2b1a6d-e550-0410-aec6-3dcde31c8c00