Implement a simple InstructionVisitor class.

Implement a simple InstructionVisitor class.

The instruction visitor visits each block and for each block each
instruction.  Rewrite the instruction printing code to use this new
visitor.

R=srdjan@google.com
BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=4547

[Kevin Millikin (Google), 2012-02-23 15:46:29]

This is based on http://codereview.chromium.org/9454012/ and includes the code
from that change (sorry: I didn't figure out a better way to do it).

I'll land them in the proper order.

I'm not sure this is the ideal approach, but we need more than one instance to
decide.

[srdjan, 2012-02-23 16:53:34]

On 2012/02/23 15:46:29, kmillikin wrote:
> This is based on http://codereview.chromium.org/9454012/ and includes the code
> from that change (sorry: I didn't figure out a better way to do it).
> 
> I'll land them in the proper order.
> 
> I'm not sure this is the ideal approach, but we need more than one instance to
> decide.

LGTM after addressing the comments of http://codereview.chromium.org/9454012/

[srdjan, 2012-02-23 16:53:52]

LGTM after addressing the issues in http://codereview.chromium.org/9454012/