Add Map constructors taking iterables.

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 88776c12721b4d2bbd29211a4879799c4d8539bc..67bc8927abba7c5dde144b1b6eb36da3654d0e3d 100644
--- a/sdk/lib/core/map.dart
+++ b/sdk/lib/core/map.dart
@@ -20,6 +20,35 @@ abstract class Map<K, V> {
   factory Map.from(Map<K, V> other) => new HashMap<K, V>.from(other);
 
   /**
+   * Creates a [Map] associating the given [keys] to [values].
+   *
+   * This constructor iterates over [keys] and [values] and maps each element of
+   * [keys] to the corresponding element of [values].
+   *
+   * If [keys] contains the same object multiple times, the last occurrence
+   * overwrites the previous value.
+   *
+   * It is an error if the two [Iterable]s don't have the same length.
+   */
+  factory Map.fromIterables(Iterable<K> keys, Iterable<V> values)
+      = HashMap<K, V>.fromIterables;
+
+  /**
+   * Creates a [Map] 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.
+   *
+   * The keys of the key/value pairs do not need to be unique. The last
+   * occurrence of a key will simply overwrite any previous value.
+   *
+   * If no values are specified for [key] and [value] the default is the
+   * identity function.
+   */
+  factory Map.fromIterable(Iterable iterable,
+      {K key(element), V value(element)}) = HashMap<K, V>.fromIterable;
+
+  /**
    * Returns whether this map contains the given [value].
    */
   bool containsValue(Object value);