Factor out some common logic from the launchers.

lib/src/runner/browser/chrome.dart

Index: lib/src/runner/browser/chrome.dart
diff --git a/lib/src/runner/browser/chrome.dart b/lib/src/runner/browser/chrome.dart
index 4d4bdaf13680d19b75dc613471ba6e4a6e909f79..351c49025025257f0a422b3187639072bd930ff5 100644
--- a/lib/src/runner/browser/chrome.dart
+++ b/lib/src/runner/browser/chrome.dart
@@ -5,19 +5,14 @@
 library test.runner.browser.chrome;
 
 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/io.dart';
-import '../../utils.dart';
-import '../application_exception.dart';
 import 'browser.dart';
 
 // TODO(nweiz): move this into its own package?
-// TODO(nweiz): support other browsers.
 /// A class for running an instance of Chrome.
 ///
 /// Most of the communication with the browser is expected to happen via HTTP,
@@ -25,79 +20,41 @@ import 'browser.dart';
 /// constructed, and is killed when [close] is called.
 ///
 /// Any errors starting or running the process are reported through [onExit].
-class Chrome implements Browser {
-  /// The underlying process.
-  Process _process;
-
-  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();
+class Chrome extends Browser {
+  final name = "Chrome";
 
   /// Starts a new instance of Chrome open to the given [url], which may be a
   /// [Uri] or a [String].
   ///
   /// If [executable] is passed, it's used as the Chrome executable. Otherwise
   /// the default executable name for the current OS will be used.
-  Chrome(url, {String executable}) {
-    if (executable == null) executable = _defaultExecutable();
-
-    // 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 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"
-          ]);
-
-          _process = process;
-          _onProcessStartedCompleter.complete();
+  Chrome(url, {String executable})
+      : super(() => _startBrowser(url, executable));
 
-          // TODO(nweiz): the browser's standard output is almost always useless
-          // noise, but we should allow the user to opt in to seeing it.
-          return await _process.exitCode;
-        });
-
-        if (exitCode != 0) {
-          var error = await UTF8.decodeStream(_process.stderr);
-          throw new ApplicationException(
-              "Chrome 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 Chrome: ${getErrorMessage(error)}."),
-            stackTrace);
-      }
-    });
-  }
-
-  Future close() {
-    _onProcessStarted.then((_) => _process.kill());
+  static Future<Process> _startBrowser(url, [String executable]) async {
+    if (executable == null) executable = _defaultExecutable();
 
-    // Swallow exceptions. The user should explicitly use [onExit] for these.
-    return onExit.catchError((_) {});
+    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"
+    ]);
+
+    process.exitCode
+        .then((_) => new Directory(dir).deleteSync(recursive: true));
+
+    return process;
   }
 
   /// Return the default executable for the current operating system.
-  String _defaultExecutable() {
+  static String _defaultExecutable() {
     if (Platform.isMacOS) {
       return '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome';
     }