Roll Observatory packages and add a roll script

packages/csslib/lib/src/tree.dart

 // 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.
 
 part of csslib.visitor;
 
 /////////////////////////////////////////////////////////////////////////
 // CSS specific types:
 /////////////////////////////////////////////////////////////////////////
 
@@ skipping 1405 matching lines @@
 
   PaddingExpression._merge(
       PaddingExpression x, PaddingExpression y, SourceSpan span)
       : super(DartStyleExpression.paddingStyle, span,
           new BoxEdge.merge(x.box, y.box));
 
   PaddingExpression clone() => new PaddingExpression(span,
       top: box.top, right: box.right, bottom: box.bottom, left: box.left);
   visit(VisitorBase visitor) => visitor.visitPaddingExpression(this);
 }