Reapply r9192 and 9194, with the change of making locale a public field.

Reapply r9192 and 9194, with the change of making locale a public field.
Committed: https://code.google.com/p/dart/source/detail?r=9206

[Emily Fortuna, 2012-06-28 00:05:31]

This CL is identical to https://chromiumcodereview.appspot.com//10692018 and
https://chromiumcodereview.appspot.com//10698025 with the additional change of
making "locale" public (because dartc doesn't like this._locale to be in the
constructor because "a named parameter can't start with _", but "this" is not in
scope if you give the parameter a name. 

Seemed like there was no reason we needed to keep "locale" private..., right?

[Alan Knight, 2012-06-28 00:09:50]

The only reason to have it private was to have it return a default locale if it
hadn't been set. I think having it private with a getter that does that is
probably the best answer. Public is probably ok in the short term.

[Emily Fortuna, 2012-06-28 16:51:21]

ptal

[Alan Knight, 2012-06-28 16:59:33]

lgtm