Package map source factory support [FIXED].

pkg/analyzer/lib/file_system/physical_file_system.dart

Index: pkg/analyzer/lib/file_system/physical_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index d9497df78ae7cdbbc3da69bd8202cdd4ddca8af9..b8fdcf17199a71049c05b49f9765d16bfa873e2d 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -41,13 +41,17 @@ class PhysicalResourceProvider implements ResourceProvider {
   Context get pathContext => io.Platform.isWindows ? windows : posix;
 
   @override
+  File getFile(String path) => new _PhysicalFile(new io.File(path));
+
+  @override
+  Folder getFolder(String path) => new _PhysicalFolder(new io.Directory(path));
+
+  @override
   Resource getResource(String path) {
     if (io.FileSystemEntity.isDirectorySync(path)) {
-      io.Directory directory = new io.Directory(path);
-      return new _PhysicalFolder(directory);
+      return getFolder(path);
     } else {
-      io.File file = new io.File(path);
-      return new _PhysicalFile(file);
+      return getFile(path);
     }
   }