code: function addTickmarks(curEditor, posArray) {
          console.assert(editor === curEditor);
  
          marks = marks.concat(posArray);
          _renderMarks(posArray);
      }
docs: Add tickmarks to the editor's tickmark track, if it's visible
  @param curEditor {!Editor}
  @param posArray {!Array.<{line:Number, ch:Number}>}