Add addAll to Map interface.

sdk/lib/core/map.dart

Index: sdk/lib/core/map.dart
diff --git a/sdk/lib/core/map.dart b/sdk/lib/core/map.dart
index fe68fd844ee39e60090c0b26091c21f06a58d709..4f67ea1e946d96a083da99a0e82cb89a86cbf672 100644
--- a/sdk/lib/core/map.dart
+++ b/sdk/lib/core/map.dart
@@ -19,7 +19,6 @@ abstract class Map<K, V> {
    */
   factory Map.from(Map<K, V> other) => new HashMap<K, V>.from(other);
 
-
   /**
    * Returns whether this map contains the given [value].
    */
@@ -54,6 +53,17 @@ abstract class Map<K, V> {
   V putIfAbsent(K key, V ifAbsent());
 
   /**
+   * Adds all key-value pairs of [other] to this map.
+   *
+   * If a key of [other] is already in this map, its value is overwritten.
+   *
+   * The operation is equivalent to doing `this[key] = value` for each key
+   * and associated value in other. It iterates over [other], which must
+   * therefore not change during the iteration.
+   */
+  void addAll(Map<K, V> other);
+
+  /**
    * Removes the association for the given [key]. Returns the value for
    * [key] in the map or null if [key] is not in the map. Note that values
    * can be null and a returned null value does not always imply that the