Corrected name clash in _posixNormalizePath.
Corrected name clash in _posixNormalizePath.

Review URL: https://codereview.chromium.org/1094583002

luisvt/reflectable,jakemac53/reflectable,bwu-dart-contributing/reflectable,luisvt/reflectable,jakemac53/reflectable,google/reflectable.dart,google/reflectable.dart,bwu-dart-contributing/reflectable