Add writeString method to OutputStream

Add writeString method to OutputStream

All output streams now supports writeString which takes the encoding
to be used when transforming the string into a sequence of bytes.

This change also introduces an Encoding interface and Encodings class
as a repository for the supported encodings. Currently this is only
UTF-8, ISO-8859-1 and ASCII. All methods in dart:io which previously
used a String to represent the encoding now uses objects implementing
Encoding.

In this change dart:io is still using the internal UTF-8 encoder used
by the HTTP implementation. I will look into using the one in dart:utf
in a separate change.

R=ager@google.com

BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=5231

[Mads Ager (google), 2012-03-09 11:22:50]

https://chromiumcodereview.appspot.com/9653026/diff/1/runtime/bin/file.dart
File runtime/bin/file.dart (right):

https://chromiumcodereview.appspot.com/9653026/diff/1/runtime/bin/file.dart#n...
runtime/bin/file.dart:9: class FileMode {
Maybe we can use this style for Encoding as well? I think we should make them
consistent.

https://chromiumcodereview.appspot.com/9653026/diff/1/runtime/bin/file.dart#n...
runtime/bin/file.dart:279: * string cannot be written the [onError] is called.
The default
This is my fault, could you fix it? ;-)

the [onError] function is called

or

[onError] is called

[Mads Ager (google), 2012-03-09 11:22:59]

Oh and LGTM!

[Søren Gjesse, 2012-03-09 13:49:25]

http://codereview.chromium.org/9653026/diff/1/runtime/bin/file.dart
File runtime/bin/file.dart (right):

http://codereview.chromium.org/9653026/diff/1/runtime/bin/file.dart#newcode9
runtime/bin/file.dart:9: class FileMode {
On 2012/03/09 11:22:50, Mads Ager wrote:
> Maybe we can use this style for Encoding as well? I think we should make them
> consistent.

Done.

http://codereview.chromium.org/9653026/diff/1/runtime/bin/file.dart#newcode279
runtime/bin/file.dart:279: * string cannot be written the [onError] is called.
The default
On 2012/03/09 11:22:50, Mads Ager wrote:
> This is my fault, could you fix it? ;-)
> 
> the [onError] function is called
> 
> or
> 
> [onError] is called

Done.