Fix order of mixin application during class finalization

runtime/vm/class_finalizer.cc

Index: runtime/vm/class_finalizer.cc
===================================================================
--- runtime/vm/class_finalizer.cc	(revision 19153)
+++ runtime/vm/class_finalizer.cc	(working copy)
@@ -1215,6 +1215,12 @@
   if (!super_class.IsNull()) {
     FinalizeClass(super_class);
   }
+  if (cls.mixin() != Type::null()) {
+    // Copy instance methods and fields from the mixin class.
+    // This has to happen before the check whether the methods of
+    // the class conflict with inherited methods.
+    ApplyMixin(cls);
+  }
   // Finalize type parameters before finalizing the super type.
   FinalizeTypeParameters(cls);
   // Finalize super type.
@@ -1248,12 +1254,6 @@
     FinalizeType(cls, sig_type, kCanonicalizeWellFormed);
     return;
   }
-  if (cls.mixin() != Type::null()) {
-    // Copy instance methods and fields from the mixin class.
-    // This has to happen before the check whether the methods of
-    // the class conflict with inherited methods.
-    ApplyMixin(cls);
-  }
   // Finalize interface types (but not necessarily interface classes).
   Array& interface_types = Array::Handle(cls.interfaces());
   AbstractType& interface_type = AbstractType::Handle();