Add tool to visualize machine code/lithium.

Add tool to visualize machine code/lithium.

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.

Originally reviewed in this CL: https://codereview.chromium.org/24957003/

Committed: http://code.google.com/p/v8/source/detail?r=17295

[danno, 2013-10-21 13:36:08]

Committed patchset #1 manually as r17295.