Add test for native mixin fields and fix the implementation.

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, 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 js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 863 matching lines @@
                                       bool needsSetter,
                                       bool needsCheckedSetter)) {
     assert(invariant(classElement, classElement.isDeclaration));
     // If the class is never instantiated we still need to set it up for
     // inheritance purposes, but we can simplify its JavaScript constructor.
     bool isInstantiated =
         compiler.codegenWorld.instantiatedClasses.contains(classElement);
 
     void visitField(ClassElement enclosingClass, Element member) {
       assert(invariant(classElement, member.isDeclaration));
-
       LibraryElement library = member.getLibrary();
       SourceString name = member.name;
       bool isPrivate = name.isPrivate();
+
+      // If we're dealing with a native class and we've found the
+      // field in an applied mixin, we treat it as if we've found the
+      // field in the class itself.
+      if (classElement.isNative() && enclosingClass.isMixinApplication) {
+        enclosingClass = classElement;
+      }
+
       // See if we can dynamically create getters and setters.
       // We can only generate getters and setters for [classElement] since
       // the fields of super classes could be overwritten with getters or
       // setters.
       bool needsGetter = false;
       bool needsSetter = false;
       // We need to name shadowed fields differently, so they don't clash with
       // the non-shadowed field.
       bool isShadowed = false;
       if (identical(enclosingClass, classElement)) {
@@ skipping 1390 matching lines @@
 """;
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;