Roll Observatory packages and add a roll script

collection/lib/iterable_zip.dart

-// Copyright (c) 2013, 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.
-
-/**
- * Zipping multiple iterables into one iterable of tuples of values.
- */
-library dart.pkg.collection.iterable_zip;
-
-import "dart:collection" show IterableBase;
-
-/**
- * Iterable that iterates over lists of values from other iterables.
- *
- * When [iterator] is read, an [Iterator] is created for each [Iterable] in
- * the [Iterable] passed to the constructor.
- *
- * As long as all these iterators have a next value, those next values are
- * combined into a single list, which becomes the next value of this
- * [Iterable]'s [Iterator]. As soon as any of the iterators run out,
- * the zipped iterator also stops.
- */
-class IterableZip extends IterableBase<List> {
-  final Iterable<Iterable> _iterables;
-  IterableZip(Iterable<Iterable> iterables)
-      : this._iterables = iterables;
-
-  /**
-   * Returns an iterator that combines values of the iterables' iterators
-   * as long as they all have values.
-   */
-  Iterator<List> get iterator {
-    List iterators = _iterables.map((x) => x.iterator).toList(growable: false);
-    // TODO(lrn): Return an empty iterator directly if iterators is empty?
-    return new _IteratorZip(iterators);
-  }
-}
-
-class _IteratorZip implements Iterator<List> {
-  final List<Iterator> _iterators;
-  List _current;
-  _IteratorZip(List iterators) : _iterators = iterators;
-  bool moveNext() {
-    if (_iterators.isEmpty) return false;
-    for (int i = 0; i < _iterators.length; i++) {
-      if (!_iterators[i].moveNext()) {
-        _current = null;
-        return false;
-      }
-    }
-    _current = new List(_iterators.length);
-    for (int i = 0; i < _iterators.length; i++) {
-      _current[i] = _iterators[i].current;
-    }
-    return true;
-  }
-
-  List get current => _current;
-}