Update {,Linked}Hash{Set,Map} documentation.

sdk/lib/collection/linked_hash_map.dart

Index: sdk/lib/collection/linked_hash_map.dart
diff --git a/sdk/lib/collection/linked_hash_map.dart b/sdk/lib/collection/linked_hash_map.dart
index e1bca0f509645ba2441fb12b13028ee64768bc1c..e06f9e6644ea24573404a6f588965713579689d4 100644
--- a/sdk/lib/collection/linked_hash_map.dart
+++ b/sdk/lib/collection/linked_hash_map.dart
@@ -43,6 +43,25 @@ abstract class LinkedHashMap<K, V> implements HashMap<K, V> {
    * The [isValidKey] function defaults to just testing if the object is a
    * [K] instance.
    *
+   * Example:
+   *
+   *     new LinkedHashMap<int,int>(equals: (int a, int b) => (b - a) % 5 == 0,
+   *                                hashCode: (int e) => e % 5)
+   *
+   * This example map does not need an `isValidKey` function to be passed.
+   * The default function accepts only `int` values, which can safely be
+   * passed to both the `equals` and `hashCode` functions.
+   *
+   * If neither `equals`, `hashCode`, nor `isValidKey` is provided,
+   * the default `isValidKey` instead accepts all keys.
+   * The default equality and hashcode operations are assumed to work on all
+   * objects.
+   *
+   * Likewise, if `equals` is [identical], `hashCode` is [identityHashCode]
+   * and `isValidKey` is omitted, the resulting map is identity based,
+   * and the `isValidKey` defaults to accepting all keys.
+   * Such a map can be created directly using [LinkedHashMap.identity].
+   *
    * The used `equals` and `hashCode` method should always be consistent,
    * so that if `equals(a, b)` then `hashCode(a) == hashCode(b)`. The hash
    * of an object, or what it compares equal to, should not change while the
@@ -50,19 +69,18 @@ abstract class LinkedHashMap<K, V> implements HashMap<K, V> {
    *
    * If you supply one of [equals] and [hashCode],
    * you should generally also to supply the other.
-   * An example would be using [identical] and [identityHashCode],
-   * which is equivalent to using the shorthand [LinkedHashMap.identity]).
    */
-  external factory LinkedHashMap({ bool equals(K key1, K key2),
-                                   int hashCode(K key),
-                                   bool isValidKey(potentialKey) });
+  external factory LinkedHashMap({bool equals(K key1, K key2),
+                                  int hashCode(K key),
+                                  bool isValidKey(potentialKey)});
 
   /**
    * Creates an insertion-ordered identity-based map.
    *
    * Effectively a shorthand for:
    *
-   *     new LinkedHashMap(equals: identical, hashCode: identityHashCodeOf)
+   *     new LinkedHashMap(equals: identical,
+   *                       hashCode: identityHashCodeOf)
    */
   external factory LinkedHashMap.identity();