Factor out some common logic from the launchers.

lib/src/runner/browser/phantom_js.dart

Index: lib/src/runner/browser/phantom_js.dart
diff --git a/lib/src/runner/browser/phantom_js.dart b/lib/src/runner/browser/phantom_js.dart
index 06247008d05b0f94a8299dd94ab0a71b96bec941..9776d9b4c7f3372f9ff409b749ae3306a910b819 100644
--- a/lib/src/runner/browser/phantom_js.dart
+++ b/lib/src/runner/browser/phantom_js.dart
@@ -5,15 +5,12 @@
 library test.runner.browser.phantom_js;
 
 import 'dart:async';
-import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
-import 'package:stack_trace/stack_trace.dart';
 
 import '../../util/exit_codes.dart' as exit_codes;
 import '../../util/io.dart';
-import '../../utils.dart';
 import '../application_exception.dart';
 import 'browser.dart';
 
@@ -39,77 +36,42 @@ page.open(system.args[1], function(status) {
 /// A class for running an instance of PhantomJS.
 ///
 /// Any errors starting or running the process are reported through [onExit].
-class PhantomJS implements Browser {
-  /// The underlying process.
-  Process _process;
+class PhantomJS extends Browser {
+  final name = "PhantomJS";
 
-  Future get onExit => _onExitCompleter.future;
-  final _onExitCompleter = new Completer();
-
-  /// A future that completes when the browser process has started.
-  ///
-  /// This is used to ensure that [close] works regardless of when it's called.
-  Future get _onProcessStarted => _onProcessStartedCompleter.future;
-  final _onProcessStartedCompleter = new Completer();
+  PhantomJS(url, {String executable})
+      : super(() => _startBrowser(url, executable));
 
   /// Starts a new instance of PhantomJS open to the given [url], which may be a
   /// [Uri] or a [String].
   ///
   /// If [executable] is passed, it's used as the PhantomJS executable.
   /// Otherwise the default executable name for the current OS will be used.
-  PhantomJS(url, {String executable}) {
+  static Future<Process> _startBrowser(url, [String executable]) async {
     if (executable == null) {
       executable = Platform.isWindows ? "phantomjs.exe" : "phantomjs";
     }
 
-    // Don't return a Future here because there's no need for the caller to wait
-    // for the process to actually start. They should just wait for the HTTP
-    // request instead.
-    invoke(() async {
-      try {
-        var exitCode = await withTempDir((dir) async {
-          var script = p.join(dir, "script.js");
-          new File(script).writeAsStringSync(_script);
-
-          var process = await Process.start(
-              executable, [script, url.toString()]);
-
-          // 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 await _process.exitCode;
-        });
-
-        if (exitCode == exit_codes.protocol) {
-          throw new ApplicationException(
-              "Only PhantomJS version 2.0.0 or greater is supported");
-        }
-
-        if (exitCode != 0) {
-          var error = await UTF8.decodeStream(_process.stderr);
-          throw new ApplicationException(
-              "PhantomJS failed with exit code $exitCode:\n$error");
-        }
-
-        _onExitCompleter.complete();
-      } catch (error, stackTrace) {
-        if (stackTrace == null) stackTrace = new Trace.current();
-        _onExitCompleter.completeError(
-            new ApplicationException(
-                "Failed to start PhantomJS: ${getErrorMessage(error)}."),
-            stackTrace);
+    var dir = createTempDir();
+    var script = p.join(dir, "script.js");
+    new File(script).writeAsStringSync(_script);
+
+    var process = await Process.start(
+        executable, [script, url.toString()]);
+
+    // PhantomJS synchronously emits standard output, which means that if we
+    // don't drain its stdout stream it can deadlock.
+    process.stdout.listen((_) {});
+
+    process.exitCode.then((exitCode) {
+      new Directory(dir).deleteSync(recursive: true);
+
+      if (exitCode == exit_codes.protocol) {
+        throw new ApplicationException(
+            "Only PhantomJS version 2.0.0 or greater is supported");
       }
     });
-  }
-
-  Future close() {
-    _onProcessStarted.then((_) => _process.kill());
 
-    // Swallow exceptions. The user should explicitly use [onExit] for these.
-    return onExit.catchError((_) {});
+    return process;
   }
 }