Improve i18n date/time test performance

Improve i18n date/time test performance
Committed: https://code.google.com/p/dart/source/detail?r=10986

[Alan Knight, 2012-08-17 20:06:49]

It was annoying me that the date/time tests took so long to run, so did some
profiling.

Caching recently used date formats turned out not to be useful, at least not
with the existing test suite. Removing a bunch of unnecessary work from a loop
in the tests helped the most. Also, converting one test to use a regex instead
of character testing slowed down very slightly in the VM but was noticeably
faster in Javascript, which seems more important right now, so switched it.

I know you're swamped right now, this is definitely not urgent.

[Emily Fortuna, 2012-08-18 00:46:30]

lgtm, with suggestion

https://chromiumcodereview.appspot.com/10836319/diff/1/pkg/i18n/lib/date_form...
File pkg/i18n/lib/date_format_helpers.dart (right):

https://chromiumcodereview.appspot.com/10836319/diff/1/pkg/i18n/lib/date_form...
pkg/i18n/lib/date_format_helpers.dart:131: // but makes a moderate difference in
Javascript right now.
perhaps we could do something a little fancier like find the first non-digit
character using a regular expression, and parse that set of digit charaters
together, so we're not always going digit by digit.