implement ES6 modules in JS AST.

lib/src/js/module_transform.dart

Index: lib/src/js/module_transform.dart
diff --git a/lib/src/js/module_transform.dart b/lib/src/js/module_transform.dart
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+// Copyright (c) 2015, 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.
+
+part of js_ast;
+
+/**
+ * Transforms EcmaScript 6 modules to an ES 5 file using a module pattern.
+ *
+ * There are various module patterns in JavaScript, see
+ * <http://babeljs.io/docs/usage/modules/> for some examples.
+ *
+ * At the moment, we only support our "custom Dart" conversion, roughly similar
+ * to Asynchronous Module Definition (AMD), see also
+ * <http://requirejs.org/docs/whyamd.html>. Like AMD, module files can
+ * be loaded directly in the browser with no further transformation (e.g.
+ * browserify, webpack).
+ */
+// TODO(jmesserly): deprecate the "custom dart" form in favor of AMD.
+class CustomDartModuleTransform extends BaseVisitor {
+  // TODO(jmesserly): implement these. Module should transform to Program.
+  visitImportDeclaration(ImportDeclaration node) {}
+  visitExportDeclaration(ExportDeclaration node) {}
+  visitModule(Module node) {}
+}