Check enums in switch cases.

pkg/compiler/lib/src/elements/modelx.dart

Index: pkg/compiler/lib/src/elements/modelx.dart
diff --git a/pkg/compiler/lib/src/elements/modelx.dart b/pkg/compiler/lib/src/elements/modelx.dart
index fbffa06d55267a19963a1b67bb0d401a609ab3ce..c5bef9020db1a91507c22df92bc86d7eb8eb1a8d 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -2414,8 +2414,9 @@ abstract class ClassElementX extends BaseClassElementX {
   }
 }
 
-class EnumClassElementX extends ClassElementX {
+class EnumClassElementX extends ClassElementX implements EnumClassElement {
   final Enum node;
+  Iterable<FieldElement> enumValuesCache;
 
   EnumClassElementX(String name, Element enclosing, int id, this.node)
       : super(name, enclosing, id, STATE_NOT_STARTED);
@@ -2433,9 +2434,21 @@ class EnumClassElementX extends ClassElementX {
   Node parseNode(Compiler compiler) => node;
 
   @override
-  accept(ElementVisitor visitor) => visitor.visitClassElement(this);
+  accept(ElementVisitor visitor) => visitor.visitEnumClassElement(this);
 
   List<DartType> computeTypeParameters(Compiler compiler) => const <DartType>[];
+
+  Iterable<FieldElement> get enumValues {
+    assert(invariant(this, enumValuesCache != null,
+        message: "enumValues has not been computed for $this."));
+    return enumValuesCache;
+  }
+
+  void set enumValues(Iterable<FieldElement> values) {
+    assert(invariant(this, enumValuesCache == null,
+        message: "enumValues has already been computed for $this."));
+    enumValuesCache = values;
+  }
 }
 
 class EnumConstructorElementX extends ConstructorElementX {