gistfile1.js

      var upload_url = presigned_s3_url;
      console.log($scope.files);

      $upload.http({
        url: upload_url,
        file: $scope.files,
        method: 'PUT',
        headers: {
          'Content-Type': 'image/png'
        }
      })
      .then(function (response) {
        console.log(response);
      })