Fix http test

tests/compiler/dart2js/launch_helper.dart

+import 'dart:async';
+import 'dart:io';
+import 'package:path/path.dart' as path;
+
+Future launchDart2Js(args,
+    {bool noStdoutEncoding: false}) {
+  String basePath = path.fromUri(Platform.script);
+  while (path.basename(basePath) != 'sdk') {
+    basePath = path.dirname(basePath);
+  }
+  String dart2jsPath = path.normalize(
+      path.join(basePath, 'pkg/compiler/lib/src/dart2js.dart'));
+  List allArgs = [];
+  if (Platform.packageRoot != null) {
+    allArgs.add('--package-root=${Platform.packageRoot}');
+  } else if (Platform.packageConfig != null) {
+    allArgs.add('--packages=${Platform.packageConfig}');
+  }
+  allArgs.add(dart2jsPath);
+  allArgs.addAll(args);
+  if (noStdoutEncoding) {
+    return Process.run(Platform.executable, allArgs, stdoutEncoding: null);
+  } else {
+    return Process.run(Platform.executable, allArgs);
+  }
+}
+