Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/utf/src/list_range.dart

Index: observatory_pub_packages/utf/src/list_range.dart
===================================================================
--- observatory_pub_packages/utf/src/list_range.dart	(revision 0)
+++ observatory_pub_packages/utf/src/list_range.dart	(working copy)
@@ -0,0 +1,79 @@
+// 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.
+
+library utf.list_range;
+
+import 'dart:collection';
+
+/**
+ * _ListRange in an internal type used to create a lightweight Interable on a
+ * range within a source list. DO NOT MODIFY the underlying list while
+ * iterating over it. The results of doing so are undefined.
+ */
+// TODO(floitsch): Consider removing the extend and switch to implements since
+// that's cheaper to allocate.
+class ListRange extends IterableBase {
+  final List _source;
+  final int _offset;
+  final int _length;
+
+  ListRange(source, [offset = 0, length]) :
+      this._source = source,
+      this._offset = offset,
+      this._length = (length == null ? source.length - offset : length) {
+    if (_offset < 0 || _offset > _source.length) {
+      throw new RangeError.value(_offset);
+    }
+    if (_length != null && (_length < 0)) {
+      throw new RangeError.value(_length);
+    }
+    if (_length + _offset > _source.length) {
+      throw new RangeError.value(_length + _offset);
+    }
+  }
+
+  ListRangeIterator get iterator =>
+      new _ListRangeIteratorImpl(_source, _offset, _offset + _length);
+
+  int get length => _length;
+}
+
+/**
+ * The ListRangeIterator provides more capabilities than a standard iterator,
+ * including the ability to get the current position, count remaining items,
+ * and move forward/backward within the iterator.
+ */
+abstract class ListRangeIterator implements Iterator<int> {
+  bool moveNext();
+  int get current;
+  int get position;
+  void backup([by]);
+  int get remaining;
+  void skip([count]);
+}
+
+class _ListRangeIteratorImpl implements ListRangeIterator {
+  final List<int> _source;
+  int _offset;
+  final int _end;
+
+  _ListRangeIteratorImpl(this._source, int offset, this._end)
+      : _offset = offset - 1;
+
+  int get current => _source[_offset];
+
+  bool moveNext() => ++_offset < _end;
+
+  int get position => _offset;
+
+  void backup([int by = 1]) {
+    _offset -= by;
+  }
+
+  int get remaining => _end - _offset - 1;
+
+  void skip([int count = 1]) {
+    _offset += count;
+  }
+}