Don't exit test script on an error in the http server.

tools/testing/dart/http_server.dart

Index: tools/testing/dart/http_server.dart
===================================================================
--- tools/testing/dart/http_server.dart	(revision 17127)
+++ tools/testing/dart/http_server.dart	(working copy)
@@ -73,11 +73,8 @@
     var httpServer = new HttpServer();
     var packagesDirName = 'packages';
     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.
+      // TODO(ricow): Once we have a debug log we should write this out there.
       print('Test http server error: $e');
-      exit(1);
     };
     httpServer.defaultRequestHandler = (request, resp) {
       var requestPath = new Path(request.path.substring(1)).canonicalize();