Extend Iterable instead of implementing it.

sdk/lib/core/iterable.dart

Index: sdk/lib/core/iterable.dart
diff --git a/sdk/lib/core/iterable.dart b/sdk/lib/core/iterable.dart
index 603a9df1a1e5ef04a740d127c4dcb83b6f97685b..f3cfa9354aa126d6d0df399dae4b52ca623f6c24 100644
--- a/sdk/lib/core/iterable.dart
+++ b/sdk/lib/core/iterable.dart
@@ -15,6 +15,8 @@
  * be used as the right-hand side of a for-in construct.
  */
 abstract class Iterable<E> {
+  const Iterable();
+
   /**
    * Returns an [Iterator] that iterates over this [Iterable] object.
    */
@@ -28,7 +30,13 @@ abstract class Iterable<E> {
    * to return a collection of the same general type as themselves.
    * E.g., [List.mappedBy] should return a [List].
    */
-  Collection mappedBy(f(E element));
+  Collection mappedBy(f(E element)) {
+    // TODO(floitsch): this is just a temporary function to provide a complete
+    // skeleton. It will be changed to become lazy soon.
+    List result = [];
+    for (E element in this) result.add(f(element));
+    return result;
+  }
 
   /**
    * Returns a collection with the elements of this collection
@@ -40,7 +48,13 @@ abstract class Iterable<E> {
    * An element satisfies the predicate [f] if [:f(element):]
    * returns true.
    */
-  Collection<E> where(bool f(E element));
+  Collection<E> where(bool f(E element)) {
+    // TODO(floitsch): this is just a temporary function to provide a complete
+    // skeleton. It will be changed to become lazy soon.
+    List result = <E>[];
+    for (E element in this) if (f(element)) result.add(element);
+    return result;
+  }
 
   /**
    * Check whether the collection contains an element equal to [element].
@@ -69,8 +83,8 @@ abstract class Iterable<E> {
    *
    *   collection.reduce(0, (prev, element) => prev + element);
    */
-  Dynamic reduce(var initialValue,
-                 Dynamic combine(var previousValue, E element)) {
+  dynamic reduce(var initialValue,
+                 dynamic combine(var previousValue, E element)) {
     var value = initialValue;
     for (E element in this) value = combine(value, element);
     return value;