Make .enclosingClass always return the declaration

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 4d5c79d551e6a1944692724c4979e6b399a108b7..6ff57cc0812853b7b839771819081f406764dea4 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -163,7 +163,7 @@ abstract class ElementX extends Element with ElementCommon {
 
   ClassElement get enclosingClass {
     for (Element e = this; e != null; e = e.enclosingElement) {
-      if (e.isClass) return e;
+      if (e.isClass) return e.declaration;
     }
     return null;
   }
@@ -2357,7 +2357,7 @@ abstract class ConstructorElementX extends FunctionElementX
 
   ConstructorElement get definingConstructor => null;
 
-  ClassElement get enclosingClass => enclosingElement;
+  ClassElement get enclosingClass => enclosingElement.declaration;
 }
 
 class DeferredLoaderGetterElementX extends GetterElementX