Big merge from experimental to bleeding edge.

tests/corelib/iterable_length_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+class A extends Iterable {
+  int count;
+  A(this.count);
+
+  Iterator get iterator {
+    return new AIterator(count);
+  }
+}
+
+class AIterator implements Iterator {
+  int _count;
+  int _current;
+
+  AIterator(this._count);
+
+  bool moveNext() {
+    if (_count > 0) {
+      _current = _count;
+      _count--;
+      return true;
+    }
+    _current = null;
+    return false;
+  }
+
+  get current => _current;
+}
+
+main() {
+  var a = new A(10);
+  Expect.equals(10, a.length);
+  a = new A(0);
+  Expect.equals(0, a.length);
+  a = new A(5);
+  Expect.equals(5, a.mappedBy((e) => e + 1).length);
+  Expect.equals(3, a.where((e) => e >= 3).length);
+}