Clean up some warnings and deprecated calls.

utils/pub/git_source.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.
 
 library git_source;
 
 import 'dart:async';
 import 'git.dart' as git;
 import 'io.dart';
 import 'package.dart';
@@ skipping 61 matching lines @@
       throw new FormatException("The description must be a Git URL or a map "
           "with a 'url' key.");
     }
     description = new Map.from(description);
     description.remove('url');
     description.remove('ref');
     if (fromLockFile) description.remove('resolved-ref');
 
     if (!description.isEmpty) {
       var plural = description.length > 1;
-      var keys = Strings.join(description.keys, ', ');
+      var keys = description.keys.join(', ');
       throw new FormatException("Invalid key${plural ? 's' : ''}: $keys.");
     }
   }
 
   /// Two Git descriptions are equal if both their URLs and their refs are
   /// equal.
   bool descriptionsEqual(description1, description2) {
     // TODO(nweiz): Do we really want to throw an error if you have two
     // dependencies on some repo, one of which specifies a ref and one of which
     // doesn't? If not, how do we handle that case in the version solver?
@@ skipping 94 matching lines @@
     return description['ref'];
   }
 
   /// Returns [description] if it's a description, or [PackageId.description] if
   /// it's a [PackageId].
   _getDescription(description) {
     if (description is PackageId) return description.description;
     return description;
   }
 }