Restructure pkg/unittest and pkg/webdriver to follow the pub conventions.

tests/standalone/io/http_server_handler_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");
-#import("dart:isolate");
+import 'dart:io';
+import 'dart:isolate';
 
 class Handler1 {
   void onRequest(HttpRequest request, HttpResponse response) {
     response.outputStream.writeString("Handler 1");
     response.outputStream.close();
   }
 }
 
 class Handler2 {
   void onRequest(HttpRequest request, HttpResponse response) {
@@ skipping 160 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();
 }