Roll Observatory packages and add a roll script

web_components/lib/src/normalize_path.dart

-// Copyright (c) 2015, 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 web_components.src.normalizePath;
-
-import 'package:path/path.dart' as path;
-
-String normalizeHtmlImportPath(
-    String filePath, String dartFilePackage, String dartFilePath) {
-  // If they already supplied a packages path, just return that.
-  if (filePath.startsWith('package:')) {
-    return filePath.replaceFirst('package:', 'packages/');
-  }
-
-  var dartFileDir = path.url.dirname(dartFilePath);
-
-  // Relative paths have no package supplied.
-  if (dartFilePackage == null) {
-    return path.url.normalize(path.url.join(dartFileDir, filePath));
-  }
-
-  // Only option left is a packages/ path.
-  return path.url.normalize(
-      path.url.join('packages/', dartFilePackage, dartFileDir, filePath));
-}