function resizeCanvasToDisplaySize(canvas, multiplier) {
    multiplier = multiplier || 1;
    multiplier = Math.max(1, multiplier);
    var width  = canvas.clientWidth  * multiplier | 0;
    var height = canvas.clientHeight * multiplier | 0;
    if (canvas.width !== width ||
        canvas.height !== height) {
      canvas.width = width;
      canvas.height = height;
      return true;
    }
    return false;
  }
Resize a canvas to match the size it's displayed.
@param {HTMLCanvasElement} canvas The canvas to resize.
@param {number} [multiplier] So you can pass in `window.devicePixelRatio` if you want to.
@return {boolean} true if the canvas was resized.
@memberOf module:twgl