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..600217a2edafc48ecec6f80bea5d4a58a224153d 100644
--- a/sdk/lib/core/map.dart
+++ b/sdk/lib/core/map.dart
@@ -20,6 +20,28 @@ abstract class Map<K, V> {
   factory Map.from(Map<K, V> other) => new HashMap<K, V>.from(other);
 
   /**
+   * Creates a map where each key is an element from [keys] with

[floitsch, 2013/06/27 11:45:04]

Try a shorter first sentence. More details in the next paragraph.

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 ...

[zarah, 2013/06/27 13:02:43]

Done.

+   * its associated value being the element from [values] at the same position.
+   *
+   * The length of [keys] and [values] must be the same, otherwise an ArgumentError

[floitsch, 2013/06/27 11:45:04]

long line.

We usually don't say what kind of error happens:

"It is an error if the two [Iterable]s don't have the same length".

[zarah, 2013/06/27 13:02:43]

Done.

+   * is thrown.
+   */
+  factory Map.fromIterables(Iterable<K> keys, Iterable<V> values)
+      = HashMap<K, V>.fromIterables;
+
+  /**
+   * Creates a map where each key-value pair is computed from each element in

[floitsch, 2013/06/27 11:45:04]

Creates a [Map] where the keys and values are computed from the [iterable].
// new line to have a separate paragraph in the doc.
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 ...

[zarah, 2013/06/27 13:02:43]

Done.

+   * [iterable]. The key is computed by applying the [key] function to the
+   * element and the value is computed by applying the [value] function to the
+   * same element.
+   *
+   * 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);