Typing fixes to eliminate casts/dcalls

tool/input_sdk/lib/collection/hash_map.dart

Index: tool/input_sdk/lib/collection/hash_map.dart
diff --git a/tool/input_sdk/lib/collection/hash_map.dart b/tool/input_sdk/lib/collection/hash_map.dart
index e67fa77556fc9a1d531dd39824e2ea8506922692..003cd4f18c8b642fe3df060d72093d26a57fb77c 100644
--- a/tool/input_sdk/lib/collection/hash_map.dart
+++ b/tool/input_sdk/lib/collection/hash_map.dart
@@ -5,9 +5,9 @@
 part of dart.collection;
 
 /** Default function for equality comparison in customized HashMaps */
-bool _defaultEquals(a, b) => a == b;
+bool _defaultEquals(Object a, Object b) => a == b;
 /** Default function for hash-code computation in customized HashMaps */
-int _defaultHashCode(a) => a.hashCode;
+int _defaultHashCode(Object a) => a.hashCode;
 
 /** Type of custom equality function */
 typedef bool _Equality<K>(K a, K b);