Fix HttpHeaders.date and add HttpHeaders.ifModifiedSince.

tests/standalone/io/http_headers_test.dart

 // Copyright (c) 2012, 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.
 
 #source("../../../runtime/bin/input_stream.dart");
 #source("../../../runtime/bin/output_stream.dart");
 #source("../../../runtime/bin/chunked_stream.dart");
 #source("../../../runtime/bin/string_stream.dart");
 #source("../../../runtime/bin/stream_util.dart");
 #source("../../../runtime/bin/http.dart");
@@ skipping 83 matching lines @@
   headers.set(HttpHeaders.EXPIRES, httpDate1);
   Expect.equals(1, headers[HttpHeaders.EXPIRES].length);
   Expect.equals(date1, headers.expires);
   Expect.equals(httpDate1, headers.value(HttpHeaders.EXPIRES));
 
   headers.set(HttpHeaders.EXPIRES, "xxx");
   Expect.equals("xxx", headers.value(HttpHeaders.EXPIRES));
   Expect.equals(null, headers.expires);
 }
 
+void testIfModifiedSince() {
+  Date date1 = new Date(1999, Date.JUN, 11, 18, 46, 53, 0, isUtc: true);
+  String httpDate1 = "Fri, 11 Jun 1999 18:46:53 GMT";
+  Date date2 = new Date(2000, Date.AUG, 16, 12, 34, 56, 0, isUtc: true);
+  String httpDate2 = "Wed, 16 Aug 2000 12:34:56 GMT";
+
+  _HttpHeaders headers = new _HttpHeaders();
+  Expect.isNull(headers.ifModifiedSince);
+  headers.ifModifiedSince = date1;
+  Expect.equals(date1, headers.ifModifiedSince);
+  Expect.equals(httpDate1, headers.value(HttpHeaders.IF_MODIFIED_SINCE));
+  Expect.equals(1, headers[HttpHeaders.IF_MODIFIED_SINCE].length);
+  headers.add(HttpHeaders.IF_MODIFIED_SINCE, httpDate2);
+  Expect.equals(1, headers[HttpHeaders.IF_MODIFIED_SINCE].length);
+  Expect.equals(date2, headers.ifModifiedSince);
+  Expect.equals(httpDate2, headers.value(HttpHeaders.IF_MODIFIED_SINCE));
+  headers.set(HttpHeaders.IF_MODIFIED_SINCE, httpDate1);
+  Expect.equals(1, headers[HttpHeaders.IF_MODIFIED_SINCE].length);
+  Expect.equals(date1, headers.ifModifiedSince);
+  Expect.equals(httpDate1, headers.value(HttpHeaders.IF_MODIFIED_SINCE));
+
+  headers.set(HttpHeaders.IF_MODIFIED_SINCE, "xxx");
+  Expect.equals("xxx", headers.value(HttpHeaders.IF_MODIFIED_SINCE));
+  Expect.equals(null, headers.ifModifiedSince);
+}
+
 void testHost() {
   String host = "www.google.com";
   _HttpHeaders headers = new _HttpHeaders();
   Expect.isNull(headers.host);
   Expect.isNull(headers.port);
   headers.host = host;
   Expect.equals(host, headers.value(HttpHeaders.HOST));
   headers.port = 1234;
   Expect.equals("$host:1234", headers.value(HttpHeaders.HOST));
   headers.port = HttpClient.DEFAULT_HTTP_PORT;
@@ skipping 241 matching lines @@
 void testInvalidCookie() {
   Expect.throws(() => new _Cookie.fromSetCookieValue(""));
   Expect.throws(() => new _Cookie.fromSetCookieValue("="));
   Expect.throws(() => new _Cookie.fromSetCookieValue("=xxx"));
   Expect.throws(() => new _Cookie.fromSetCookieValue("xxx"));
   Expect.throws(() => new _Cookie.fromSetCookieValue("xxx=yyy; expires=12 jan 2013"));
 }
 
 main() {
   testMultiValue();
+  testDate();
   testExpires();
+  testIfModifiedSince();
   testHost();
   testEnumeration();
   testHeaderValue();
   testContentType();
   testContentTypeCache();
   testCookie();
   testInvalidCookie();
 }