Roll Observatory packages and add a roll script

packages/source_maps/lib/src/vlq.dart

 // Copyright (c) 2013, 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.
 
 
 /// Utilities to encode and decode VLQ values used in source maps.
 ///
 /// Sourcemaps are encoded with variable length numbers as base64 encoded
 /// strings with the least significant digit coming first. Each base64 digit
 /// encodes a 5-bit value (0-31) and a continuation bit. Signed values can be
@@ skipping 83 matching lines @@
   result = result >> 1;
   result = negate ? -result : result;
 
   // TODO(sigmund): can we detect this earlier?
   if (result < MIN_INT32 || result > MAX_INT32) {
     throw new FormatException(
         'expected an encoded 32 bit int, but we got: $result');
   }
   return result;
 }