Improve equivalence testing of unnamed mixin applications.

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

Index: pkg/compiler/lib/src/elements/elements.dart
diff --git a/pkg/compiler/lib/src/elements/elements.dart b/pkg/compiler/lib/src/elements/elements.dart
index dc708d0d6076dd1899c236011970172a360baaae..28812931a6c737f994893d8da9170eda8485ab4d 100644
--- a/pkg/compiler/lib/src/elements/elements.dart
+++ b/pkg/compiler/lib/src/elements/elements.dart
@@ -1526,6 +1526,10 @@ abstract class ClassElement extends TypeDeclarationElement
 abstract class MixinApplicationElement extends ClassElement {
   ClassElement get mixin;
   InterfaceType get mixinType;
+
+  /// If this is an unnamed mixin application [subclass] is the subclass for
+  /// which this mixin application is created.
+  ClassElement get subclass;
 }
 
 /// Enum declaration.