Begin refactoring compiler out of diet parser and scanner

pkg/compiler/lib/src/id_generator.dart

Index: pkg/compiler/lib/src/id_generator.dart
diff --git a/pkg/compiler/lib/src/id_generator.dart b/pkg/compiler/lib/src/id_generator.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4c92ea9dbfa69023c9908c80dd778e111b3ae0dd
--- /dev/null
+++ b/pkg/compiler/lib/src/id_generator.dart
@@ -0,0 +1,13 @@
+// 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.
+
+/// A generator of globally unique identifiers.
+class IdGenerator {
+  int _nextFreeId = 0;
+
+  /// Returns the next free identifier.
+  ///
+  /// This identifier is guaranteed to be unique.
+  int getNextFreeId() => _nextFreeId++;
+}