switch package to strong mode

lib/assets.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.
 
 /// Common methods used by transfomers for dealing with asset IDs.
 library code_transformers.assets;
 
 import 'dart:math' show min, max;
 
 import 'package:barback/barback.dart';
@@ skipping 65 matching lines @@
     } else if (index == 1 && segments[0] == '..') {
       // Relative URLs of the form "../../packages/foo/bar" in an asset under
       // lib/ or asset/ are also resolved as an asset in another package, but we
       // check that the relative path goes all the way out where the packages
       // folder lives (otherwise the app would not work in Dartium). Since
       // [targetPath] has been normalized, "packages" or "assets" should be at
       // index 1.
       return _extractOtherPackageId(1, segments, logger, span);
     } else {
       var prefix = segments[index];
-      var fixedSegments = [];
+      var fixedSegments = <String>[];
       fixedSegments.addAll(sourceSegments.map((_) => '..'));
       fixedSegments.addAll(segments.sublist(index));
       var fixedUrl = urlBuilder.joinAll(fixedSegments);
       var msg = INVALID_URL_TO_OTHER_PACKAGE
           .create({'url': url, 'prefix': prefix, 'fixedUrl': fixedUrl});
       logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
       return null;
     }
   }
 
   // Otherwise, resolve as a path in the same package.
   return new AssetId(source.package, targetPath);
 }
 
 AssetId _extractOtherPackageId(
-    int index, List segments, TransformLogger logger, SourceSpan span) {
+    int index, List<String> segments, TransformLogger logger, SourceSpan span) {
   if (index >= segments.length) return null;
   var prefix = segments[index];
   if (prefix != 'packages' && prefix != 'assets') return null;
   var folder = prefix == 'packages' ? 'lib' : 'asset';
   if (segments.length < index + 3) {
     var msg = INVALID_PREFIX_PATH.create({'prefix': prefix, 'folder': folder});
     logger.warning(logger is BuildLogger ? msg : msg.snippet, span: span);
     return null;
   }
   return new AssetId(segments[index + 1],
@@ skipping 28 matching lines @@
     }
     return new Uri(
             path: path.url.relative(assetId.path, from: path.url.dirname(from.path)))
         .toString();
   }
 
   return Uri
       .parse('package:${assetId.package}/${assetId.path.substring(4)}')
       .toString();
 }