code: function makeViewportGetter_(dimension, inner, client) {
    if (testMQ('(min-' + dimension + ':' + window[inner] + 'px)')) {
      return function getWindowDimension_() {
        return window[inner];
      };
    } else {
      var docElem = document.documentElement;
      return function getDocumentDimension_() {
        return docElem[client];
      };
    }
  }
docs: Return a function which gets the viewport width or height.
  @private
  @param {String} dimension The dimension to look up.
  @param {String} inner The inner dimension.
  @param {String} client The client dimension.
  @return {function} The getter function.