Add "contains" method to Collection.

Add "contains" method to Collection.

This versions does not implement "contains" on DOM lists.

Committed: https://code.google.com/p/dart/source/detail?r=13806

[Lasse Reichstein Nielsen, 2012-10-18 11:25:38]

Reapplying without changes to html-lib templates. The HTML lists won't implement
contains yet.

CC'ing people who might be able to add it (q.v.
https://codereview.chromium.org/11186045/ for changes that almost did it).

[floitsch, 2012-10-18 11:48:09]

LGTM.

[sra1, 2012-10-19 02:26:29]

On 2012/10/18 11:25:38, Lasse Reichstein Nielsen wrote:
> Reapplying without changes to html-lib templates. The HTML lists won't
implement
> contains yet.
> 
> CC'ing people who might be able to add it (q.v.
> https://codereview.chromium.org/11186045/ for changes that almost did it).

https://codereview.chromium.org/11187063/ is the cl with the html changes + a
couple of tests.
It needs to be checked in after this CL since the tests rely on JSArray having
'contains'.

[ahe, 2012-10-19 07:58:23]

What happened to dart:core being a library of few essential concepts?

Why do we need seven different classes to represent the concept which is
essentially a "list"?

Why does every user of Dart need to know the difference between "List",
"Iterator", "Collection", "Sequence", "SequenceCollection", "SequenceList", and
"SequenceIterator"?

Are you aware that each class you define in dart:core is by default imported
into all libraries?

Could you explain why a "sequence" implies unmodifiable? Could you explain why
we don't need a four more classes to model lists that can only be written to?