Support using the HEAD request in the HTTP library

tests/standalone/io/http_head_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.
+
+#import("dart:io");
+
+void testHEAD(int totalConnections) {
+  HttpServer server = new HttpServer();
+  server.onError = (e) => Expect.fail("Unexpected error $e");
+  server.listen("127.0.0.1", 0, totalConnections);
+  server.addRequestHandler(
+      (request) => request.path == "/test100",
+      (HttpRequest request, HttpResponse response) {
+        response.contentLength = 100;
+        response.outputStream.close();
+      });
+  server.addRequestHandler(
+      (request) => request.path == "/test200",
+      (HttpRequest request, HttpResponse response) {
+        response.contentLength = 200;
+        List<int> data = new Uint32List(200);
+        response.outputStream.write(data);
+        response.outputStream.close();
+      });
+
+  HttpClient client = new HttpClient();
+
+  int count = 0;
+  for (int i = 0; i < totalConnections; i++) {
+    HttpClientConnection conn;
+    int len = (i % 2 == 0) ? 100 : 200;
+    if (i % 2 == 0) {
+      conn = client.open("HEAD", "127.0.0.1", server.port, "/test$len");
+    } else {
+      conn = client.open("HEAD", "127.0.0.1", server.port, "/test$len");
+    }
+    conn.onError = (e) => Expect.fail("Unexpected error $e");
+    conn.onResponse = (HttpClientResponse response) {
+      Expect.equals(len, response.contentLength);
+      response.inputStream.onData = () => Expect.fail("Data from HEAD request");
+      response.inputStream.onClosed = () {
+        count++;
+        if (count == totalConnections) {
+          client.shutdown();
+          server.close();
+        }
+      };
+    };
+  }
+}
+
+void main() {
+  testHEAD(4);
+}