Make the VM's dart:core and dart:async library patches clean.

runtime/lib/core_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:async";
 import "dart:collection" show LinkedList, LinkedListEntry;
 import 'dart:convert' show ASCII, JSON;
 import "dart:isolate";
 import "dart:math";
 import "dart:typed_data";
 import 'dart:_internal' as internal;
 
 // Equivalent of calling FATAL from C++ code.
 _fatal(msg) native "DartCore_fatal";
 
 // The members of this class are cloned and added to each class that
 // represents an enum type.
 class _EnumHelper {
   String _name;
   String toString() => _name;
   int get hashCode => _name.hashCode;
 }
 
 // _SyncIterable and _syncIterator are used by the compiler to
 // implement sync* generator functions. A sync* generator allocates
 // and returns a new _SyncIterable object.
 
-typedef bool SyncGeneratorCallback(Iterator iterator);
+typedef bool _SyncGeneratorCallback(Iterator iterator);
 
 class _SyncIterable extends IterableBase {
   // moveNextFn is the closurized body of the generator function.
-  final SyncGeneratorCallback moveNextFn;
+  final _SyncGeneratorCallback moveNextFn;

[Lasse Reichstein Nielsen, 2016/12/08 12:25:32]

Not your CL, but ...
I don't think this field should be public. The class leaks and users can see the
field if they do `print(()sync*{}().moveNextFn)`. Same for iterator.

[Kevin Millikin (Google), 2016/12/09 08:38:59]

That should be noncontroversial, so I'll just change it here and below.

 
   const _SyncIterable(this.moveNextFn);
 
   get iterator {
     return new _SyncIterator(moveNextFn._clone());
   }
 }
 
 class _SyncIterator implements Iterator {
   bool isYieldEach;  // Set by generated code for the yield* statement.
   Iterator yieldEachIterator;
   var _current;  // Set by generated code for the yield and yield* statement.
-  SyncGeneratorCallback moveNextFn;
+  _SyncGeneratorCallback moveNextFn;

[Lasse Reichstein Nielsen, 2016/12/08 12:25:32]

All of these should be private, the user gets access to the object.
(Again, you don't have to fix it, but somebody will have to).

 
   get current => yieldEachIterator != null
       ? yieldEachIterator.current
       : _current;
 
   _SyncIterator(this.moveNextFn);
 
   bool moveNext() {
     if (moveNextFn == null) {
       return false;
@@ skipping 20 matching lines @@
         continue;
       }
       return true;
     }
   }
 }
 
 @patch class StackTrace {
   @patch static StackTrace get current native "StackTrace_current";
 }