Make pub strong-mode clean.

test/descriptor/packages.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.
 
 /// Pub-specific scheduled_test descriptors.
 import "dart:io" show File;
 import "dart:async" show Future;
 import "dart:convert" show UTF8;
 
 import 'package:package_config/packages_file.dart' as packages_file;
@@ skipping 17 matching lines @@
   /// Describes a `.packages` file with the given dependencies.
   ///
   /// [dependencies] maps package names to strings describing where the packages
   /// are located on disk.
   PackagesFileDescriptor([this._dependencies]) : super('.packages');
 
   Future create([String parent]) => schedule(() {
     if (parent == null) parent = defaultRoot;
     var contents = const <int>[];
     if (_dependencies != null) {
-      var mapping = {};
+      var mapping = <String, Uri>{};
       _dependencies.forEach((package, version) {
         var packagePath;
         if (_semverRE.hasMatch(version)) {
           // If it's a semver, it's a cache reference.
           packagePath = p.join(cachePath, "$package-$version");
         } else {
           // Otherwise it's a path relative to the pubspec file,
           // which is also relative to the .packages file.
           packagePath = p.fromUri(version);
         }
@@ skipping 55 matching lines @@
       for (var key in map.keys) {
         if (!_dependencies.containsKey(key)) {
           fail(".packages file contains unexpected entry: $key");
         }
       }
     }
   }
 
   String describe() => name;
 }