Properly return Windows-formatted paths from package.listFiles.

sdk/lib/_internal/pub/lib/src/io.dart

Index: sdk/lib/_internal/pub/lib/src/io.dart
diff --git a/sdk/lib/_internal/pub/lib/src/io.dart b/sdk/lib/_internal/pub/lib/src/io.dart
index 8aae3e213fb86078c81776dc5b80749fa9cbe2f1..4d4ddd5a7101b40d7db0a264dcf20d384ef83196 100644
--- a/sdk/lib/_internal/pub/lib/src/io.dart
+++ b/sdk/lib/_internal/pub/lib/src/io.dart
@@ -303,10 +303,7 @@ List<String> listDir(String dir, {bool recursive: false,
     if (pathInDir.contains("/.")) return false;
     if (Platform.operatingSystem != "windows") return true;
     return !pathInDir.contains("\\.");
-  }).map((entity) {
-    if (Platform.operatingSystem != "windows") return entity.path;
-    return entity.path.replaceAll("/", "\\");
-  }).toList();
+  }).map((entity) => entity.path).toList();
 }
 
 /// Returns whether [dir] exists on the file system.