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

runtime/lib/core_patch.dart

Index: runtime/lib/core_patch.dart
diff --git a/runtime/lib/core_patch.dart b/runtime/lib/core_patch.dart
index 29357aec4d8fe7c873d5323cb5646c592c3cf382..b6d933375ae0eccacf0084b514eb703a3b42fb23 100644
--- a/runtime/lib/core_patch.dart
+++ b/runtime/lib/core_patch.dart
@@ -25,11 +25,11 @@ class _EnumHelper {
 // 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);
 
@@ -42,7 +42,7 @@ 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