Update charted to 0.4.8 and roll

packages/collection/lib/src/combined_wrappers/combined_iterable.dart

+// Copyright (c) 2017, 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.
+
+import 'dart:collection';
+
+/// A view of several iterables combined sequentially into a single iterable.
+///
+/// All methods and accessors treat the [CombinedIterableView] as if it were a
+/// single concatenated iterable, but the underlying implementation is based on
+/// lazily accessing individual iterable instances. This means that if the
+/// underlying iterables change, the [CombinedIterableView] will reflect those
+/// changes.
+class CombinedIterableView<T> extends IterableBase<T> {
+  /// The iterables that this combines.
+  final Iterable<Iterable<T>> _iterables;
+
+  /// Creates a combined view of [iterables].
+  const CombinedIterableView(this._iterables);
+
+  Iterator<T> get iterator =>
+      new _CombinedIterator<T>(_iterables.map((i) => i.iterator).iterator);
+
+  // Special cased contains/isEmpty/length since many iterables have an
+  // efficient implementation instead of running through the entire iterator.
+
+  bool contains(Object element) => _iterables.any((i) => i.contains(element));
+
+  bool get isEmpty => _iterables.every((i) => i.isEmpty);
+
+  int get length => _iterables.fold(0, (length, i) => length + i.length);
+}
+
+/// The iterator for [CombinedIterableView].
+///
+/// This moves through each iterable's iterators in sequence.
+class _CombinedIterator<T> implements Iterator<T> {
+  /// The iterators that this combines.
+  ///
+  /// Because this comes from a call to [Iterable.map], it's lazy and will
+  /// avoid instantiating unnecessary iterators.
+  final Iterator<Iterator<T>> _iterators;
+
+  _CombinedIterator(this._iterators);
+
+  T get current => _iterators.current?.current;
+
+  bool moveNext() {
+    var current = _iterators.current;
+    if (current != null && current.moveNext()) {
+      return true;
+    }
+    return _iterators.moveNext() && moveNext();
+  }
+}