Better mirrors support for mixins and private fields

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart

 // Copyright (c) 2015, 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.
 
 /// This library defines the operations that define and manipulate Dart
 /// classes.  Included in this are:
 ///   - Generics
 ///   - Class metadata
 ///   - Extension methods
 ///
@@ skipping 46 matching lines @@
   });
 
   // Save mixins for reflection
   Mixin[$_mixins] = $mixins;
   return Mixin;
 })()''');
 
 /// The Symbol for storing type arguments on a specialized generic type.
 final _mixins = JS('', 'Symbol("mixins")');
 
-getMixins(clazz) => JS('', '$clazz[$_mixins]');
+getMixins(clazz) => JS('', 'Object.hasOwnProperty.call(#, #) ? #[#] : null', clazz, _mixins, clazz, _mixins);
 
 @JSExportName('implements')
 final _implements = JS('', 'Symbol("implements")');
 
-getImplements(clazz) => JS('', '#[#]', clazz, _implements);
+getImplements(clazz) => JS('', 'Object.hasOwnProperty.call(#, #) ? #[#] : null', clazz, _implements, clazz, _implements);
 
 /// The Symbol for storing type arguments on a specialized generic type.
 final _typeArguments = JS('', 'Symbol("typeArguments")');
 
 final _originalDeclaration = JS('', 'Symbol("originalDeclaration")');
 
 /// Wrap a generic class builder function with future flattening.
 flattenFutures(builder) => JS(
     '',
     '''(() => {
@@ skipping 465 matching lines @@
     '''(() => {
   let values = [];
   for (var i = 0; i < $names.length; i++) {
     let value = $const_(new $enumClass(i));
     values.push(value);
     Object.defineProperty($enumClass, $names[i],
         { value: value, configurable: true });
   }
   $enumClass.values = $constList(values, $enumClass);
 })()''');