Getting enums for free.

lib/kernel_visitor.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.md file.
 
 library rasta.kernel_visitor;
 
 import 'package:kernel/ast.dart' as ir;
 
 import 'package:kernel/accessors.dart' show
     Accessor,
@@ skipping 748 matching lines @@
     return buildBreakTarget(
         new ir.DoStatement(body, condition), node, jumpTarget);
   }
 
   @override
   ir.EmptyStatement visitEmptyStatement(EmptyStatement node) {
     return new ir.EmptyStatement();
   }
 
   @override
-  ir.Throw visitEnum(Enum node) {
-    return buildUnsupported(node, "Enum");
+  visitEnum(Enum node) {
+    // Not called normally. In dart2js, enums are represented as class
+    // elements, so `classToIr` handles enums.  All the synthetic members of an
+    // enum class have already been installed by dart2js and we don't have to
+    // do anything special.
+    return internalError(node, "Enum");
   }
 
   @override
   ir.ExpressionStatement visitExpressionStatement(ExpressionStatement node) {
     return new ir.ExpressionStatement(visitForEffect(node.expression));
   }
 
   @override
   ir.Statement visitFor(For node) {
     VariableDefinitions initializers =
@@ skipping 2268 matching lines @@
       : this(null, true, node, initializers);
 
   accept(ir.Visitor v) => throw "unsupported";
 
   visitChildren(ir.Visitor v) => throw "unsupported";
 
   String toString() {
     return "IrFunction($kind, $isConstructor, $node, $initializers)";
   }
 }