Support enums in dart2dart.

pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart

Index: pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart b/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
index c2381f685fec5cb1e3daeeb68daccd32bfdb6026..373ccfd41371b09a8ff9ab8362225da3afd68a8f 100644
--- a/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
@@ -139,6 +139,7 @@ class TreePrinter {
   final Token withToken = makeIdToken('with');
   final Token implementsToken = makeIdToken('implements');
   final Token typedefToken = makeIdToken('typedef');
+  final Token enumToken = makeIdToken('enum');
 
   static tree.Identifier makeIdentifier(String name) {
     return new tree.Identifier(
@@ -1060,6 +1061,8 @@ class TreePrinter {
   tree.Node makeNodeForClassElement(elements.ClassElement cls) {
     if (cls.isMixinApplication) {
       return makeNamedMixinApplication(cls);
+    } else if (cls.isEnumClass) {
+      return makeEnum(cls);
     } else {
       return makeClassNode(cls);
     }
@@ -1181,6 +1184,14 @@ class TreePrinter {
         interfaces, classToken, semicolon);
   }
 
+  tree.Enum makeEnum(elements.EnumClassElement cls) {
+    return new tree.Enum(
+        enumToken,
+        makeIdentifier(cls.name),
+        makeList(',', cls.enumValues.map((e) => makeIdentifier(e.name)),
+                 open: openBrace, close: closeBrace));
+  }
+
   /// Creates a [tree.ClassNode] node for [cls].
   tree.ClassNode makeClassNode(elements.ClassElement cls) {
     assert(dart2js.invariant(cls, !cls.isUnnamedMixinApplication,