Roll Observatory packages and add a roll script

packages/html/lib/src/utils.dart

 /// Misc things that were useful when porting the code from Python.
 library utils;
 
 import 'constants.dart';
 
 typedef bool Predicate();
 
 class Pair<F, S> {
   final F first;
   final S second;
@@ skipping 103 matching lines @@
 
       last = match + 1;
     }
 
     result.write(format.substring(last, format.length));
     format = result.toString();
   });
 
   return format;
 }