We used to rely on reading both POSITION and STATEMENT_POSITION to get
correct decoding of positions. This was error prone and made liveedit
unhappy.

Review URL: http://codereview.chromium.org/5277007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5905 ce2b1a6d-e550-0410-aec6-3dcde31c8c00