Roll Observatory packages and add a roll script

packages/source_span/lib/src/utils.dart

 // Copyright (c) 2014, 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 source_span.utils;
 
 /// Returns the minimum of [obj1] and [obj2] according to
 /// [Comparable.compareTo].
 Comparable min(Comparable obj1, Comparable obj2) =>
     obj1.compareTo(obj2) > 0 ? obj2 : obj1;
@@ skipping 13 matching lines @@
   while (index != -1) {
     var lineStart = context.lastIndexOf('\n', index) + 1;
     var textColumn = index - lineStart;
     if (column == textColumn || (isEmpty && column == textColumn + 1)) {
       return lineStart;
     }
     index = context.indexOf(text, index + 1);
   }
   return null;
 }