Add support for passing in precompiled JS.

test/runner/precompiled_paths_test.dart

+// Copyright (c) 2016, 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.
+
+@TestOn("vm")
+@Tags(const ["chrome"])
+
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:scheduled_test/descriptor.dart' as d;
+import 'package:scheduled_test/scheduled_process.dart';
+import 'package:scheduled_test/scheduled_stream.dart';
+import 'package:scheduled_test/scheduled_test.dart';
+
+import 'package:test/src/util/io.dart';
+
+import '../io.dart';
+
+void main() {
+  useSandbox();
+
+  test("runs a precompiled version of a test rather than recompiling", () {
+    d.file("to_precompile.dart", """
+      import "package:stream_channel/stream_channel.dart";
+
+      import "package:test/src/runner/plugin/remote_platform_helpers.dart";
+      import "package:test/src/runner/browser/post_message_channel.dart";
+      import "package:test/test.dart";
+
+      main(_) async {
+        var channel = serializeSuite(() {
+          return () => test("success", () {});
+        }, hidePrints: false);
+        postMessageChannel().pipe(channel);
+      }
+    """).create();
+
+    d.dir("precompiled", []).create();
+
+    var dart2js = new ScheduledProcess.start(p.join(sdkDir, 'bin', 'dart2js'), [
+      "--package-root=${p.join(p.current, 'packages')}",
+      "to_precompile.dart",
+      "--out=precompiled/test.dart.browser_test.dart.js"
+    ], workingDirectory: sandbox);
+    dart2js.shouldExit(0);
+
+    d.file("test.dart", "invalid dart}").create();
+
+    var test = runTest(
+        ["-p", "chrome", "--precompiled=precompiled/", "test.dart"]);
+    test.stdout.expect(containsInOrder([
+      "+0: success",
+      "+1: All tests passed!"
+    ]));
+    test.shouldExit(0);
+  });
+}