Small simplification of HChange instruction.

Small simplification of HChange instruction.

Use existing flag to mark HChange instructions that deoptimize on undefined.

Also there is no need to store the source representation explicitly.
Committed: http://code.google.com/p/v8/source/detail?r=9472

[fschneider, 2011-09-28 13:42:55]

The cl looks larger than it is. It is really just a small refactoring of
HChange.

I had to change one function to not being const as a result because the
accessors in our template-instruction are also non-const.

[Jakob Kummerow, 2011-09-28 13:55:50]

LGTM