Remove the RequestHandler interface from the HTTP library

tests/standalone/src/io/HttpServerHandlerTest.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");
 #import("dart:isolate");
 
-class Handler1 implements RequestHandler {
+class Handler1 {
   void onRequest(HttpRequest request, HttpResponse response) {
     response.outputStream.writeString("Handler 1");
     response.outputStream.close();
   }
 }
 
-class Handler2 implements RequestHandler {
+class Handler2 {
   void onRequest(HttpRequest request, HttpResponse response) {
     response.outputStream.writeString("Handler 2");
     response.outputStream.close();
   }
 }
 
-class French404Handler implements RequestHandler {
+class French404Handler {
   void onRequest(HttpRequest request, HttpResponse response) {
     response.statusCode = HttpStatus.NOT_FOUND;
     response.reasonPhrase = "Non Trouvé";
     response.outputStream.close();
   }
 }
 
 class Server {
   Server() {
     server = new HttpServer();
     server.listen("127.0.0.1", 0);
     port = server.port;
     server.onError = (e) {
       Expect.fail("No server errors expected: $e");
     };
   }
 
   void addHandler(Function matcher, handler) {
-    server.addRequestHandler(matcher, handler);
+    if (handler is Function) {
+      server.addRequestHandler(matcher, handler);
+    } else {
+      server.addRequestHandler(matcher, handler.onRequest);
+    }
   }
 
   void set defaultHandler(handler) {
-    server.defaultRequestHandler = handler;
+    if (handler is Function) {
+      server.defaultRequestHandler = handler;
+    } else {
+      server.defaultRequestHandler = handler.onRequest;
+    }
   }
 
   void close() {
     server.close();
   }
 
   int port;
   HttpServer server;
 }
 
@@ skipping 113 matching lines @@
   testRequest("/yyy.dat", HttpStatus.OK, "Handler 3");
   testRequest("/abc.dat", HttpStatus.OK, "Handler 4");
   testRequest("/abcdat", HttpStatus.NOT_FOUND, "");
   testRequest("/xxx.dat", HttpStatus.OK, "Handler 2");
 }
 
 main() {
   testDefaultHandler();
   testHandlers();
 }