Add a hidden pub command to generate core library stubs.

pkg/stub_core_library/lib/src/utils.dart

Index: pkg/stub_core_library/lib/src/utils.dart
diff --git a/pkg/stub_core_library/lib/src/utils.dart b/pkg/stub_core_library/lib/src/utils.dart
new file mode 100644
index 0000000000000000000000000000000000000000..d5bdd8f4def76273473280b4864a6cf6a1730509
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+++ b/pkg/stub_core_library/lib/src/utils.dart
@@ -0,0 +1,24 @@
+// Copyright (c) 2014, 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.
+
+library stub_core_libraries.utils;
+
+/// Returns a sentence fragment listing the elements of [iter].
+///
+/// This converts each element of [iter] to a string and separates them with
+/// commas and/or "and" where appropriate.
+String toSentence(Iterable iter) {
+  if (iter.length == 1) return iter.first.toString();
+  return iter.take(iter.length - 1).join(", ") + " and ${iter.last}";
+}
+
+/// Returns [name] if [number] is 1, or the plural of [name] otherwise.
+///
+/// By default, this just adds "s" to the end of [name] to get the plural. If
+/// [plural] is passed, that's used instead.
+String pluralize(String name, int number, {String plural}) {
+  if (number == 1) return name;
+  if (plural != null) return plural;
+  return '${name}s';
+}