Add fixed content type values for commonly used content types

sdk/lib/io/http.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 /**
  * HTTP status codes.
  */
 abstract class HttpStatus {
@@ skipping 572 matching lines @@
   bool get isNew;
 }
 
 
 /**
  * Representation of a content type. An instance of [ContentType] is
  * immutable.
  */
 abstract class ContentType implements HeaderValue {
   /**
+   * Content type for plain text using UTF-8 encoding.
+   *
+   *     text/plain; charset=utf-8
+   */
+  static final TEXT = new ContentType("text", "plain", charset: "utf-8");
+
+  /**
+   *  Content type for HTML using UTF-8 encoding.
+   *
+   *     text/html; charset=utf-8
+   */
+  static final HTML = new ContentType("text", "html", charset: "utf-8");
+
+  /**
+   *  Content type for JSON using UTF-8 encoding.
+   *
+   *     application/json; charset=utf-8
+   */
+  static final JSON = new ContentType("application", "json", charset: "utf-8");
+
+  /**
+   *  Content type for binary data.
+   *
+   *     application/octet-stream
+   */
+  static final BINARY = new ContentType("application", "octet-stream");
+
+  /**
    * Creates a new content type object setting the primary type and
    * sub type. The charset and additional parameters can also be set
    * using [charset] and [parameters]. If charset is passed and
    * [parameters] contains charset as well the passed [charset] will
    * override the value in parameters. Keys and values passed in
    * parameters will be converted to lower case.
    */
   factory ContentType(String primaryType,
                       String subType,
                       {String charset, Map<String, String> parameters}) {
@@ skipping 1011 matching lines @@
 class RedirectException implements HttpException {
   final String message;
   final List<RedirectInfo> redirects;
 
   const RedirectException(this.message, this.redirects);
 
   String toString() => "RedirectException: $message";
 
   Uri get uri => redirects.last.location;
 }