Manually default Error messages to avoid dart2js code bloat.

Manually default Error messages to avoid dart2js code bloat.

The generated code with this change has 'null' arguments instead of
multiple copies of the default message string.

Ideally the compiler would recognize common code patterns and extract
them into helper code.  This requires architectural changes to the
compiler.  The nulls can be removed with an optimization (pending)
that is possible with the current architecture.

[sra1, 2014-11-11 21:22:55]

sra@google.com changed reviewers:
+ lrn@google.com

[sra1, 2014-11-11 21:23:23]

Patchset #1 (id:1) has been deleted

[Lasse Reichstein Nielsen, 2014-11-12 07:08:51]

LGTM. I think this is perfectly fine, and, on second thought, probably better.
We don't generally make a big deal out of the exact error message text, so
exposing it in the API is unnecessary.
Only change I'd make is to update the comment to say that the [message]
parameter, if provided, overides the default error description text.
That is, say that there is a default text.

[Lasse Reichstein Nielsen, 2014-11-12 07:38:43]

I've incorporated this into another CL.

[Lasse Reichstein Nielsen, 2014-11-13 12:48:34]

And it's been committed as r41705