Roll Observatory packages and add a roll script

quiver/lib/src/iterables/zip.dart

-// Copyright 2013 Google Inc. All Rights Reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-part of quiver.iterables;
-
-/**
- * Returns an [Iterable] of [List]s where the nth element in the returned
- * iterable contains the nth element from every Iterable in [iterables]. The
- * returned Iterable is as long as the shortest Iterable in the argument. If
- * [iterables] is empty, it returns an empty list.
- */
-Iterable<List> zip(Iterable<Iterable> iterables) =>
-    (iterables.isEmpty) ? const [] : new _Zip(iterables);
-
-class _Zip extends IterableBase<List> {
-  final Iterable<Iterable> iterables;
-
-  _Zip(Iterable<Iterable> this.iterables);
-
-  Iterator<List> get iterator => new _ZipIterator(
-      iterables.map((i) => i.iterator).toList(growable: false));
-}
-
-class _ZipIterator implements Iterator<List> {
-  final List<Iterator> _iterators;
-  List _current;
-
-  _ZipIterator(List<Iterator> this._iterators);
-
-  List get current => _current;
-
-  bool moveNext() {
-    bool hasNext = true;
-    var newValue = new List(_iterators.length);
-    for (int i = 0; i < _iterators.length; i++) {
-      var iter = _iterators[i];
-      hasNext = hasNext && iter.moveNext();
-      newValue[i] = iter.current;
-    }
-    _current = (hasNext) ? newValue : null;
-    return hasNext;
-  }
-}