Update test scripts to run under the Dart 1.6 vm.

tools/testing/dart/browser_controller.dart

 // Copyright (c) 2013, 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.
 library browser;
 
 import "dart:async";
 import "dart:convert" show LineSplitter, UTF8;
 import "dart:core";
 import "dart:io";
 
@@ skipping 1290 matching lines @@
         var browserId = request.uri.path.substring(startedPath.length + 1);
         var testId =
             int.parse(request.uri.queryParameters["id"].split("=")[1]);
         handleStarted(request, browserId, testId);
         return;
       }
       var textResponse = "";
       if (request.uri.path.startsWith(driverPath)) {
         var browserId = request.uri.path.substring(driverPath.length + 1);
         textResponse = getDriverPage(browserId);
+        request.response.headers.set('Content-Type', 'text/html');
       } else if (request.uri.path.startsWith(nextTestPath)) {
         var browserId = request.uri.path.substring(nextTestPath.length + 1);
         textResponse = getNextTest(browserId);
+        request.response.headers.set('Content-Type', 'text/plain');
       } else {
         // /favicon.ico requests
       }
       request.response.write(textResponse);
       request.listen((_) {}, onDone: request.response.close);
       request.response.done.catchError((error) {
           if (!underTermination) {
             print("URI ${request.uri}");
             print("Textresponse $textResponse");
             throw "Error returning content to browser: $error";
@@ skipping 278 matching lines @@
     Dart test driver, number of tests: <div id="number"></div><br>
     Currently executing: <div id="currently_executing"></div><br>
     Unhandled error: <div id="unhandled_error"></div>
     <iframe id="embedded_iframe"></iframe>
   </body>
 </html>
 """;
     return driverContent;
   }
 }