Replace dead instructions with a constant with no type

Replace dead instructions with a constant with no type

Previously the dead instructions were replaced with int 0, which
polluted the types.  There are only occasional improvements since most
optimizations happen before the first dead code elimination phase.

R=floitsch@google.com

Committed: https://code.google.com/p/dart/source/detail?r=32876

[sra1, 2014-02-05 01:12:48]

This change fixes the union type I was seeing.
Not sure if it is worth committing, but it is good to explain the weird type.

[sra1, 2014-02-05 01:12:49]

This change fixes the union type I was seeing.
Not sure if it is worth committing, but it is good to explain the weird type.

[floitsch, 2014-02-06 23:15:42]

The names are off, but otherwise LGTM.
Maybe just renaming DummyReceiverConstant to DummyConstant ?

[sra1, 2014-02-20 23:51:03]

Committed patchset #1 manually as r32876 (presubmit successful).

[floitsch, 2014-02-21 09:59:07]

You ignored my comment.
Why do you prefer keeping the current DummyReceiverConstant name?

[sra1, 2014-02-21 20:16:19]

On 2014/02/21 09:59:07, floitsch wrote:
> You ignored my comment.
> Why do you prefer keeping the current DummyReceiverConstant name?

The renaming is a much bigger change that would hide the real change.
https://codereview.chromium.org/172853007/

[floitsch, 2014-02-22 21:00:14]

On 2014/02/21 20:16:19, sra1 wrote:
> On 2014/02/21 09:59:07, floitsch wrote:
> > You ignored my comment.
> > Why do you prefer keeping the current DummyReceiverConstant name?
> 
> The renaming is a much bigger change that would hide the real change.
> https://codereview.chromium.org/172853007/

Ok. I was afraid you hadn't seen my comment (seeing my green name in the
review-view).
Should have expressed myself differently.