Add package config support to dart:isolate

tests/isolate/spawn_uri_fail_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.
+
+import "dart:io";
+import "dart:isolate";
+import "package:expect/expect.dart";
+
+main() async {
+  var pkgRoot = Uri.parse("file:///no/such/directory/");
+  var pkgConfig = Uri.parse("file:///no/such/.packages");
+  try {
+    var i = await Isolate.spawnUri(Platform.script, [], null,
+        packageRoot: pkgRoot, packageConfig: pkgConfig);
+  } catch (e) {
+    print(e);
+    Expect.isTrue(e is ArgumentError);
+  }
+  try {
+    var i = await Isolate.spawnUri(Platform.script, [], null,
+        packageRoot: pkgRoot, automaticPackageResolution: true);
+  } catch (e) {
+    print(e);
+    Expect.isTrue(e is ArgumentError);
+  }
+  try {
+    var i = await Isolate.spawnUri(Platform.script, [], null,
+        packageConfig: pkgConfig, automaticPackageResolution: true);
+  } catch (e) {
+    print(e);
+    Expect.isTrue(e is ArgumentError);
+  }
+  try {
+    var i = await Isolate.spawnUri(Platform.script, [], null,
+        packageRoot: pkgRoot, packageConfig: pkgConfig,
+        automaticPackageResolution: true);
+  } catch (e) {
+    print(e);
+    Expect.isTrue(e is ArgumentError);
+  }
+}