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

runtime/lib/immutable_map.dart

Index: runtime/lib/immutable_map.dart
diff --git a/runtime/lib/immutable_map.dart b/runtime/lib/immutable_map.dart
index ba866e39cf3769864345229f65abca18e3b5ae32..9c5699b14e6b0bf5ffea17c04da07bf2131cf7e9 100644
--- a/runtime/lib/immutable_map.dart
+++ b/runtime/lib/immutable_map.dart
@@ -3,10 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 // Immutable map class for compiler generated map literals.
 
-class ImmutableMap<K, V> implements Map<K, V> {
+class _ImmutableMap<K, V> implements Map<K, V> {
   final _ImmutableList _kvPairs;
 
-  const ImmutableMap._create(_ImmutableList keyValuePairs)
+  const _ImmutableMap._create(_ImmutableList keyValuePairs)
       : _kvPairs = keyValuePairs;