Getting enums for free.

lib/kernel_visitor.dart

Index: lib/kernel_visitor.dart
diff --git a/lib/kernel_visitor.dart b/lib/kernel_visitor.dart
index 4b9049f20c8cbe5b3601c02ad62f5303d8ff4811..2b6c00b13d79cc8680cdaa992821e291c6cbac1b 100644
--- a/lib/kernel_visitor.dart
+++ b/lib/kernel_visitor.dart
@@ -766,8 +766,12 @@ class KernelVisitor extends Object
   }
 
   @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