Make dart:collection strong-mode clean.

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;
 /** Default function for hash-code computation in customized HashMaps */
 int _defaultHashCode(a) => a.hashCode;
@@ skipping 84 matching lines @@
    *     new HashMap(equals: identical,
    *                 hashCode: identityHashCode)
    */
   external factory HashMap.identity();
 
   /**
    * Creates a [HashMap] that contains all key/value pairs of [other].
    */
   factory HashMap.from(Map other) {
     HashMap<K, V> result = new HashMap<K, V>();
-    other.forEach((k, v) { result[k] = v; });
+    other.forEach((k, v) { result[k as Object/*=K*/] = v as Object/*=V*/; });
     return result;
   }
 
   /**
    * Creates a [HashMap] where the keys and values are computed from the
    * [iterable].
    *
    * For each element of the [iterable] this constructor computes a key/value
    * pair, by applying [key] and [value] respectively.
    *
@@ skipping 20 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;
   }
 }