Add HTTP handler registration to the HTTP server

tests/standalone/src/io/HttpServerEarlyClientCloseTest.dart

 #import("dart:io");
 #import("dart:isolate");
 
 void sendData(List<int> data, int port) {
   Socket socket = new Socket("127.0.0.1", port);
   socket.onConnect = () {
     socket.onData = () {
       Expect.fail("No data response was expected");
     };
     socket.outputStream.onNoPendingWrites = () {
       socket.close(false);
     };
     socket.outputStream.write(data);
   };
 }
 
 class EarlyCloseTest {
   EarlyCloseTest(Object this.data,
                  String this.exception,
                  [bool this.expectRequest = false]);
 
   Future execute(HttpServer server) {
     Completer c = new Completer();
 
     bool calledOnRequest = false;
     bool calledOnError = false;
-    server.onRequest = (HttpRequest request, HttpResponse response) {
-      Expect.isTrue(expectRequest);
-      Expect.isFalse(calledOnError);
-      Expect.isFalse(calledOnRequest, "onRequest called multiple times");
-      calledOnRequest = true;
-    };
+    server.defaultRequestHandler =
+        (HttpRequest request, HttpResponse response) {
+          Expect.isTrue(expectRequest);
+          Expect.isFalse(calledOnError);
+          Expect.isFalse(calledOnRequest, "onRequest called multiple times");
+          calledOnRequest = true;
+        };
     ReceivePort port = new ReceivePort();
     server.onError = (Exception error) {
       Expect.isFalse(calledOnError);
       Expect.equals(exception, error.message);
       Expect.equals(expectRequest, calledOnRequest);
       calledOnError = true;
       port.close();
       c.complete(null);
     };
 
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     } else {
       server.close();
     }
   }
   runTest(tests.iterator());
 }
 
 void main() {
   testEarlyClose();
 }