Typing fixes to eliminate casts/dcalls

tool/input_sdk/lib/collection/hash_map.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.
 
 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);
 /** Type of custom hash code function. */
 typedef int _Hasher<K>(K object);
 
 /**
  * A hash-table based implementation of [Map].
  *
  * The keys of a `HashMap` must have consistent [Object.operator==]
@@ skipping 97 matching lines @@
    * overwrites the previous value.
    *
    * It is an error if the two [Iterable]s don't have the same length.
    */
   factory HashMap.fromIterables(Iterable<K> keys, Iterable<V> values) {
     HashMap<K, V> map = new HashMap<K, V>();
     Maps._fillMapWithIterables(map, keys, values);
     return map;
   }
 }