Detect an old PhantomJS and emit a nice error.

lib/src/runner/browser/phantom_js.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.phantom_js;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
+import '../../util/exit_codes.dart' as exit_codes;
 import '../../util/io.dart';
+import '../application_exception.dart';
 import 'browser.dart';
 
 /// The PhantomJS script that opens the host page.
 final _script = """
 var system = require('system');
 var page = require('webpage').create();
 
+// PhantomJS versions older than 2.0.0 don't support the latest WebSocket spec.
+if (phantom.version.major < 2) phantom.exit(${exit_codes.protocol});
+
 // Pipe browser messages to the process's stdout. This isn't used by default,
 // but it can be useful for debugging.
 page.onConsoleMessage = function(message) {
   console.log(message);
 }
 
 page.open(system.args[1], function(status) {
   if (status !== "success") phantom.exit(1);
 });
 """;
@@ skipping 36 matching lines @@
         // PhantomJS synchronously emits standard output, which means that if we
         // don't drain its stdout stream it can deadlock.
         process.stdout.listen((_) {});
 
         _process = process;
         _onProcessStartedCompleter.complete();
 
         return _process.exitCode;
       });
     }).then((exitCode) {
+      if (exitCode == exit_codes.protocol) {
+        throw new ApplicationException(
+            "Only PhantomJS version 2.0.0 or greater is supported.");
+      }
       if (exitCode != 0) throw "PhantomJS failed with exit code $exitCode.";
     }).then(_onExitCompleter.complete)
         .catchError(_onExitCompleter.completeError);
   }
 
   Future close() {
     _onProcessStarted.then((_) => _process.kill());
 
     // Swallow exceptions. The user should explicitly use [onExit] for these.
     return onExit.catchError((_) {});
   }
 }