Only fetch the Observatory URL in debug mode.

lib/src/runner/browser/dartium.dart

 // Copyright (c) 2015, 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 test.runner.browser.dartium;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
@@ skipping 12 matching lines @@
 /// Most of the communication with the browser is expected to happen via HTTP,
 /// so this exposes a bare-bones API. The browser starts as soon as the class is
 /// constructed, and is killed when [close] is called.
 ///
 /// Any errors starting or running the process are reported through [onExit].
 class Dartium extends Browser {
   final name = "Dartium";
 
   final Future<Uri> observatoryUrl;
 
-  factory Dartium(url, {String executable}) {
+  factory Dartium(url, {String executable, bool debug: false}) {
     var completer = new Completer.sync();
     return new Dartium._(() async {
       if (executable == null) executable = _defaultExecutable();
 
       var dir = createTempDir();
       var process = await Process.start(executable, [
         "--user-data-dir=$dir",
         url.toString(),
         "--disable-extensions",
         "--disable-popup-blocking",
         "--bwsi",
         "--no-first-run",
         "--no-default-browser-check",
         "--disable-default-apps",
         "--disable-translate"
       ], environment: {"DART_FLAGS": "--checked"});
 
-      // The first observatory URL emitted is for the empty start page; the
-      // second is actually for the host page.
-      completer.complete(_getObservatoryUrl(process.stdout));
+      if (debug) {
+        completer.complete(_getObservatoryUrl(process.stdout));
+      } else {
+        completer.complete(null);
+      }
 
       process.exitCode
           .then((_) => new Directory(dir).deleteSync(recursive: true));
 
       return process;
     }, completer.future);
   }
 
   Dartium._(Future<Process> startBrowser(), this.observatoryUrl)
       : super(startBrowser);
@@ skipping 178 matching lines @@
         // incorrect WebSocket that already closed.
         return null;
       }
     }).catchError((error, stackTrace) {
       if (!completer.isCompleted) completer.completeError(error, stackTrace);
     });
 
     return completer.future;
   }
 }