Make instances of HeaderValue and ContentType immutable

tests/standalone/io/http_headers_test.dart

-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 import 'dart:async';
 import 'dart:math';
 
 part "../../../sdk/lib/io/io_sink.dart";
 part "../../../sdk/lib/io/http.dart";
 part "../../../sdk/lib/io/http_headers.dart";
 part "../../../sdk/lib/io/http_impl.dart";
@@ skipping 186 matching lines @@
       });
     } else {
       Expect.equals(0, headerValue.parameters.length);
     }
   }
 
   HeaderValue headerValue;
   headerValue = new HeaderValue.fromString(
       "xxx; aaa=bbb; ccc=\"\\\";\\a\"; ddd=\"    \"");
   check(headerValue, "xxx", {"aaa": "bbb", "ccc": '\";a', "ddd": "    "});
+  headerValue = new HeaderValue("xxx",
+                                {"aaa": "bbb", "ccc": '\";a', "ddd": "    "});
+  check(headerValue, "xxx", {"aaa": "bbb", "ccc": '\";a', "ddd": "    "});
+
   headerValue = new HeaderValue.fromString(
     "attachment; filename=genome.jpeg;"
     "modification-date=\"Wed, 12 February 1997 16:29:51 -0500\"");
   var parameters = {
       "filename": "genome.jpeg",
       "modification-date": "Wed, 12 February 1997 16:29:51 -0500"
   };
   check(headerValue, "attachment", parameters);
+  headerValue = new HeaderValue("attachment", parameters);
+  check(headerValue, "attachment", parameters);
   headerValue = new HeaderValue.fromString(
     "  attachment  ;filename=genome.jpeg  ;"
     "modification-date = \"Wed, 12 February 1997 16:29:51 -0500\""  );
   check(headerValue, "attachment", parameters);
 }
 
 void testContentType() {
   void check(ContentType contentType,
              String primaryType,
              String subType,
              [Map parameters]) {
     Expect.equals(primaryType, contentType.primaryType);
     Expect.equals(subType, contentType.subType);
     Expect.equals("$primaryType/$subType", contentType.value);
     if (parameters != null) {
       Expect.equals(parameters.length, contentType.parameters.length);
       parameters.forEach((String name, String value) {
         Expect.equals(value, contentType.parameters[name]);
       });
     } else {
       Expect.equals(0, contentType.parameters.length);
     }
   }
 
   ContentType contentType;
   contentType = new ContentType();
   Expect.equals("", contentType.primaryType);
   Expect.equals("", contentType.subType);
   Expect.equals("/", contentType.value);
-  contentType.value = "text/html";
-  Expect.equals("text", contentType.primaryType);
-  Expect.equals("html", contentType.subType);
-  Expect.equals("text/html", contentType.value);
 
   contentType = new _ContentType.fromString("text/html");
   check(contentType, "text", "html");
   Expect.equals("text/html", contentType.toString());
-  contentType.parameters["charset"] = "utf-8";
+  contentType = new _ContentType.fromString("text/html; charset=utf-8");
   check(contentType, "text", "html", {"charset": "utf-8"});
   Expect.equals("text/html; charset=utf-8", contentType.toString());
   contentType.parameters["xxx"] = "yyy";
   check(contentType, "text", "html", {"charset": "utf-8", "xxx": "yyy"});
   String s = contentType.toString();
   bool expectedToString = (s == "text/html; charset=utf-8; xxx=yyy" ||
                            s == "text/html; xxx=yyy; charset=utf-8");
   Expect.isTrue(expectedToString);
 
   contentType = new _ContentType.fromString("text/html");
@@ skipping 23 matching lines @@
   _HttpHeaders headers = new _HttpHeaders("1.1");
   headers.set(HttpHeaders.CONTENT_TYPE, "text/html");
   Expect.equals("text", headers.contentType.primaryType);
   Expect.equals("html", headers.contentType.subType);
   Expect.equals("text/html", headers.contentType.value);
   headers.set(HttpHeaders.CONTENT_TYPE, "text/plain; charset=utf-8");
   Expect.equals("text", headers.contentType.primaryType);
   Expect.equals("plain", headers.contentType.subType);
   Expect.equals("text/plain", headers.contentType.value);
   headers.removeAll(HttpHeaders.CONTENT_TYPE);
-  Expect.equals("", headers.contentType.primaryType);
-  Expect.equals("", headers.contentType.subType);
-  Expect.equals("/", headers.contentType.value);
+  Expect.isNull(headers.contentType);
 }
 
 void testCookie() {
   void checkCookiesEquals(a, b) {
     Expect.equals(a.name, b.name);
     Expect.equals(a.value, b.value);
     Expect.equals(a.expires, b.expires);
     Expect.equals(a.toString(), b.toString());
   }
 
@@ skipping 91 matching lines @@
   testIfModifiedSince();
   testHost();
   testEnumeration();
   testHeaderValue();
   testContentType();
   testContentTypeCache();
   testCookie();
   testInvalidCookie();
   testHeaderLists();
 }