Make sure field initializers have access to the type variables.

sdk/lib/collection/splay_tree.dart

Index: sdk/lib/collection/splay_tree.dart
===================================================================
--- sdk/lib/collection/splay_tree.dart	(revision 19209)
+++ sdk/lib/collection/splay_tree.dart	(working copy)
@@ -227,7 +227,9 @@
  * method.
  */
 class SplayTreeMap<K, V> extends _SplayTree<K> implements Map<K, V> {
-  Comparator<K> _comparator;
+  // TODO(ngeoffray): Restore type when feature is implemented in dart2js
+  // checked mode. http://dartbug.com/7733  
+  Function /* Comparator<K> */_comparator;
 
   SplayTreeMap([int compare(K key1, K key2)])
       : _comparator = (compare == null) ? Comparable.compare : compare;