code: function filterFiles( files ){
      var filtered = [],
          file,
          i;
      for( i = 0; i < files.length; i++ ){
          file = files[ i ];
          if( file.height &&
              file.width &&
              file.url ){
              //This is sufficient to serve as a level
              filtered.push({
                  url: file.url,
                  width: Number( file.width ),
                  height: Number( file.height )
              });
          }
          else {
              $.console.error( 'Unsupported image format: %s', file.url ? file.url : '<no URL>' );
          }
      }
  
      return filtered.sort(function(a, b) {
          return a.height - b.height;
      });
  
  }
docs: This method removes any files from the Array which don't conform to our
  basic requirements for a 'level' in the LegacyTileSource.
  @private
  @inner
  @function