Add uri getter on file system entity.

sdk/lib/core/uri.dart

Index: sdk/lib/core/uri.dart
diff --git a/sdk/lib/core/uri.dart b/sdk/lib/core/uri.dart
index bbc491c7343e9ce0ea889c0c7353b809b72f43f3..3fe4100dbf366e111d90af934ba765a68b785b87 100644
--- a/sdk/lib/core/uri.dart
+++ b/sdk/lib/core/uri.dart
@@ -704,7 +704,7 @@ class Uri {
    * If the path passed is not a legal file path [ArgumentError] is thrown.
    */
   factory Uri.file(String path, {bool windows}) {
-    windows = windows == null ? Uri._isWindows : windows;
+    windows = (windows == null) ? Uri._isWindows : windows;
     return windows ? _makeWindowsFileUrl(path) : _makeFileUri(path);
   }