Native subclasses of a mixin include classes extending native classes

sdk/lib/_internal/compiler/implementation/ssa/interceptor_simplifier.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 /**
  * This phase simplifies interceptors in multiple ways:
  *
  * 1) If the interceptor is for an object whose type is known, it
@@ skipping 150 matching lines @@
 
     // If the interceptor is used by multiple instructions, specialize
     // it with a set of classes it intercepts.
     Set<ClassElement> interceptedClasses;
     JavaScriptBackend backend = compiler.backend;
     HInstruction dominator =
         findDominator(node.usedBy.where((i) => i is HInvokeDynamic));
     // If there is an instruction that dominates all others, we can
     // use only the selector of that instruction.
     if (dominator != null) {
-      interceptedClasses = 
+      interceptedClasses =
             backend.getInterceptedClassesOn(dominator.selector.name);
 
       // If we found that we need number, we must still go through all
       // uses to check if they require int, or double.
       if (interceptedClasses.contains(backend.jsNumberClass)
           && !(interceptedClasses.contains(backend.jsDoubleClass)
                || interceptedClasses.contains(backend.jsIntClass))) {
         for (var user in node.usedBy) {
           if (user is! HInvoke) continue;
           Set<ClassElement> intercepted =
@@ skipping 94 matching lines @@
       inputs[0] = constant;
       instruction = new HInvokeDynamicMethod(selector, inputs, true);
     }
 
     HBasicBlock block = node.block;
     block.addAfter(node, instruction);
     block.rewrite(node, instruction);
     return true;
   }
 }