Make instances of HeaderValue and ContentType immutable

Make instances of HeaderValue and ContentType immutable

Their parameters map is still mutable though.

R=ajohnsen@google.com

BUG=

Committed: https://code.google.com/p/dart/source/detail?r=19598

[Anders Johnsen, 2013-03-05 11:58:51]

LGTM, nice API change.

[Anders Johnsen, 2013-03-05 11:59:09]

Oh yeah, do we have a bug issue on this?

[Søren Gjesse, 2013-03-05 15:44:40]

Nathan, Bob could you please take a look at the pkg/http changes related to
making ContentType (almost) immutable.

[nweiz, 2013-03-05 20:43:18]

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/multipart...
File pkg/http/lib/src/multipart_file.dart (right):

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/multipart...
pkg/http/lib/src/multipart_file.dart:77: encoding.name);
This needs to copy all the parameters from the original content type over as
well.

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/request.dart
File pkg/http/lib/src/request.dart (right):

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/request.d...
pkg/http/lib/src/request.dart:62: value.name);
Same here.

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/request.d...
pkg/http/lib/src/request.dart:97: encoding.name);
And here.

[Søren Gjesse, 2013-03-06 13:23:30]

PTAL

I changed the constructor for ContentType and also decided to always have all
parameters (including charset) converted to lower case.

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/multipart...
File pkg/http/lib/src/multipart_file.dart (right):

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/multipart...
pkg/http/lib/src/multipart_file.dart:77: encoding.name);
On 2013/03/05 20:43:18, nweiz wrote:
> This needs to copy all the parameters from the original content type over as
> well.

Done.

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/request.dart
File pkg/http/lib/src/request.dart (right):

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/request.d...
pkg/http/lib/src/request.dart:62: value.name);
On 2013/03/05 20:43:18, nweiz wrote:
> Same here.

Done.

https://codereview.chromium.org/12440002/diff/4001/pkg/http/lib/src/request.d...
pkg/http/lib/src/request.dart:97: encoding.name);
On 2013/03/05 20:43:18, nweiz wrote:
> And here.

Done.

[Søren Gjesse, 2013-03-06 13:26:17]

Opened https://code.google.com/p/dart/issues/detail?id=8951 on the mutability
issue.

[nweiz, 2013-03-06 20:09:33]

pkg/http changes LGTM

[Søren Gjesse, 2013-03-07 07:26:08]

Committed patchset #3 manually as r19598 (presubmit successful).