Make instances of HeaderValue and ContentType immutable

tests/standalone/io/http_headers_test.dart

Index: tests/standalone/io/http_headers_test.dart
diff --git a/tests/standalone/io/http_headers_test.dart b/tests/standalone/io/http_headers_test.dart
index 19829e79954b7ac08b2ed5b4a4c075e20b866526..2f2e069058b12826ca4bf8f41f68f14b3cc1e1ba 100644
--- a/tests/standalone/io/http_headers_test.dart
+++ b/tests/standalone/io/http_headers_test.dart
@@ -1,4 +1,4 @@
-// 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.
 
@@ -205,6 +205,10 @@ void testHeaderValue() {
   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\"");
@@ -213,6 +217,8 @@ void testHeaderValue() {
       "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\""  );
@@ -242,15 +248,11 @@ void testContentType() {
   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";
@@ -294,9 +296,7 @@ void testContentTypeCache() {
   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() {