Use const instead of runtime type for equality of EmptyExpression.

Use const instead of runtime type for equality of EmptyExpression.

R=jmesserly@google.com, justinfagnani@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28042

[ngeoffray, 2013-09-27 07:55:35]

This was motivated by a hint given by dart2js (when doing build.py) that there
is operator==, but no hashCode in EmptyExpression.

I don't know if that's the right approach for you, or if you want other call
sites to use 'new' instead of 'const', but that's one way to avoid the hint, and
improve memory/performance.

[kasperl, 2013-09-27 07:58:21]

Adding Justin as a reviewer too.

[justinfagnani, 2013-09-27 19:14:59]

lgtm

const is fine for this. Thanks!

[Jennifer Messerly, 2013-09-27 19:21:58]

lgtm too, thank you Nicolas!

[ngeoffray, 2013-09-30 06:37:15]

Committed patchset #1 manually as r28042 (presubmit successful).