Port r17295 (b36eb655)

Original commit message:
In the process:
- Add a command-line flag --opt-code-positions to track source position information throughout optimized code.
- Add a subclass of the hydrogen graph builder to ensure that the source position is properly set on the graph builder for all generated hydrogen code.
- Overhaul handling of source positions in hydrogen to ensure they are passed through to generated code consistently and in most cases transparently.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/33803002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17305 ce2b1a6d-e550-0410-aec6-3dcde31c8c00