Temporary fix to mac buildbot issue. We need to figure out why

tools/testing/dart/http_server.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.
 
 #library('http_server');
 
 #import('dart:io');
+#import('dart:isolate');
 #import('test_suite.dart');  // For TestUtils.
 
 HttpServer _httpServer;
 
-startHttpServer(String host, int port) {
+// TODO(ager): Get rid of this when we get the Mac to behave.
+int _retries = 10;
+
+Future<bool> startHttpServer(String host, int port) {
+  var completer = new Completer();
   var basePath = TestUtils.dartDir();
   _httpServer = new HttpServer();
   _httpServer.onError = (e) {
     // Consider errors in the builtin http server fatal.
     // Intead of just throwing the exception we print
     // a message that makes it clearer what happened.
     print('Test http server error: $e');
     exit(1);
   };
   _httpServer.defaultRequestHandler = (request, resp) {
@@ skipping 10 matching lines @@
           // Allow loading from localhost in browsers.
           resp.headers.set("Access-Control-Allow-Origin", "*");
           file.openInputStream().pipe(resp.outputStream);
         } else {
           resp.statusCode = HttpStatus.NOT_FOUND;
           resp.outputStream.close();
         }
       });
     }
   };
-  _httpServer.listen(host, port);
+
+  // TODO(ager): Get rid of this when we get the mac to behave.
+  // Even though we have set the SO_REUSEADDR the mac is not
+  // happy and gives us address alread in use errors.
+  try {
+    _httpServer.listen(host, port);
+    completer.complete(true);
+  } catch (e) {
+    if (_retries-- == 0) {
+      completer.completeException(e);
+    }
+    new Timer(1000, (t) {
+      startHttpServer(host, port).then((r) => completer.complete(r));
+    });
+  }
+  return completer.future;
 }
 
 terminateHttpServer() {
   _httpServer.close();
 }