Better mirrors support for mixins and private fields

pkg/dev_compiler/tool/input_sdk/patch/internal_patch.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.
 
 import 'dart:_js_primitives' show printString;
 import 'dart:_js_helper' show patch;
 import 'dart:_interceptors' show JSArray;
 import 'dart:_foreign_helper' show JS;
 
 @patch
 class Symbol implements core.Symbol {
   @patch
   const Symbol(String name)
-      : this._name = name;
+      : this._name = name, this._nativeSymbol = null;
+
+  @patch
+  const Symbol.es6(String name, dynamic nativeSymbol)
+      : this._name = name, this._nativeSymbol = nativeSymbol;
 
   @patch
   int get hashCode {
     int hash = JS('int|Null', '#._hashCode', this);
     if (hash != null) return hash;
     const arbitraryPrime = 664597;
     hash = 0x1fffffff & (arbitraryPrime * _name.hashCode);
     JS('', '#._hashCode = #', this, hash);
     return hash;
   }
 }
 
 @patch
 void printToConsole(String line) {
   printString('$line');
 }
 
 @patch
 List/*<E>*/ makeListFixedLength/*<E>*/(List/*<E>*/ growableList) {
   JSArray.markFixedList(growableList);
   return growableList;
 }
 
 @patch
 List/*<E>*/ makeFixedListUnmodifiable/*<E>*/(List/*<E>*/ fixedLengthList) {
   JSArray.markUnmodifiableList(fixedLengthList);
   return fixedLengthList;
 }