assertWidth = function(a, b, opt_c) {
  'use strict';
  _validateArguments(2, arguments);
  const element = nonCommentArg(1, 2, arguments);
  const width = nonCommentArg(2, 2, arguments);
  const size = goog.style.getSize(element);
  const elementWidth = size.width;

  _assert(
      commentArg(1, arguments),
      goog.testing.style.layoutasserts.isWithinThreshold_(
          width, elementWidth, 0 /* tolerance */),
      'Element should have width ' + width + ' but was ' + elementWidth + '.');
}
Asserts that the element must have the specified width.
@param {Element|string} a The first element or optionally the comment string.
@param {Element|number} b The second element or the first element if comment string
    is present.
@param {(Element|number)=} opt_c The second element if comment string is present.