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 e58d75242743f7114a2daf0c5984288f9558ed5b..c0feddb650727cda2a8bb68114803268cd26f68b 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -2418,8 +2418,9 @@ abstract class ClassElementX extends BaseClassElementX {
   }
 }
 
-class EnumClassElementX extends ClassElementX {
+class EnumClassElementX extends ClassElementX implements EnumClassElement {
   final Enum node;
+  Iterable<FieldElement> _enumValues;
 
   EnumClassElementX(String name, Element enclosing, int id, this.node)
       : super(name, enclosing, id, STATE_NOT_STARTED);
@@ -2437,9 +2438,21 @@ 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, _enumValues != null,
+        message: "enumValues has not been computed for $this."));
+    return _enumValues;
+  }
+
+  void set enumValues(Iterable<FieldElement> values) {
+    assert(invariant(this, _enumValues == null,
+        message: "enumValues has already been computed for $this."));
+    _enumValues = values;
+  }
 }
 
 class EnumConstructorElementX extends ConstructorElementX {