Stack trace string should use dynamic script sourceURL if present.

BUG=v8:2342
R=dcarney@chromium.org, yurys@chromium.org, yurys
LOG=N

Review URL: https://codereview.chromium.org/143283015

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19333 ce2b1a6d-e550-0410-aec6-3dcde31c8c00