Refactor Source and SourceRegistry.

lib/src/validator/dependency.dart

Index: lib/src/validator/dependency.dart
diff --git a/lib/src/validator/dependency.dart b/lib/src/validator/dependency.dart
index 3caa8c264cdd80b45434bd4cfd90a7b4682bdb33..e00879ca9ebbc3fccc5008a1ab88a3f6bd234d02 100644
--- a/lib/src/validator/dependency.dart
+++ b/lib/src/validator/dependency.dart
@@ -9,7 +9,6 @@ import 'package:pub_semver/pub_semver.dart';
 import '../entrypoint.dart';
 import '../log.dart' as log;
 import '../package.dart';
-import '../source/hosted.dart';
 import '../validator.dart';
 
 /// The range of all pub versions that don't support `^` version constraints.
@@ -66,8 +65,8 @@ class DependencyValidator extends Validator {
   Future _warnAboutSource(PackageDep dep) async {
     var versions;
     try {
-      var ids = await entrypoint.cache.sources['hosted']
-          .getVersions(HostedSource.refFor(dep.name));
+      var ids = await entrypoint.cache.hosted
+          .getVersions(entrypoint.cache.sources.hosted.refFor(dep.name));
       versions = ids.map((id) => id.version).toList();
     } catch (error) {
       versions = [];