Expose the Observatory URL when debugging.

lib/src/runner/browser/browser.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.browser;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:stack_trace/stack_trace.dart';
 
 import '../../utils.dart';
 import '../application_exception.dart';
 
 typedef Future<Process> StartBrowserFn();
 
 /// An interface for running browser instances.
 ///
 /// This is intentionally coarse-grained: browsers are controlled primary from
 /// inside a single tab. Thus this interface only provides support for closing
 /// the browser and seeing if it closes itself.
 ///
 /// Any errors starting or running the browser process are reported through
 /// [onExit].
 abstract class Browser {
   String get name;
 
+  Future<Uri> get observatoryUrl =>
+      throw new UnsupportedError("$name doesn't support Observatory.");
+
   /// The underlying process.
   ///
   /// This will fire once the process has started successfully.
   Future<Process> get _process => _processCompleter.future;
   final _processCompleter = new Completer<Process>();
 
   /// Whether [close] has been called.
   var _closed = false;
 
   /// A future that completes when the browser exits.
@@ skipping 59 matching lines @@
   /// Returns the same [Future] as [onExit], except that it won't emit
   /// exceptions.
   Future close() {
     _closed = true;
     _process.then((process) => process.kill());
 
     // Swallow exceptions. The user should explicitly use [onExit] for these.
     return onExit.catchError((_) {});
   }
 }