Fix loading Windows native extension packages

Source: chromiumcodereview.appspot.com --- Sunday, August 06, 2017
Fix loading Windows native extension packages Use the standard Dart URI logic to parse the file path out from the library URI when loading a native extension. This parses the file path out correctly on Windows, which is not the case when you only strip the scheme from the URI. BUG= ...

from Windows http://ift.tt/2wyk5lU