Introduce v8::Exception::GetStackTrace API method.

This will be needed to get a stack trace from a DOMException.

API=v8::Exception::GetStackTrace
R=yangguo@chromium.org
LOG=Y

Review URL: https://codereview.chromium.org/655243002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24655 ce2b1a6d-e550-0410-aec6-3dcde31c8c00