code: function minimizeStyles(message) {
    var nestingDepth = message.frameIndex.split('.').length - 1;
    var iframe = document.createElement('iframe');
    document.body.appendChild(iframe);
    iframe.setAttribute(
        'style',
        `height: ${message.windowHeight}px;` + 
        `width: ${message.windowWidth}px;`);
  
    var html = message.html.join('');
    html = unescapeHTML(html, nestingDepth);
    iframe.contentDocument.documentElement.innerHTML = html;
    var doc = iframe.contentDocument;
  
    // Remove entry in |message.html| where extra style element was specified.
    message.html[message.pseudoElementTestingStyleIndex] = '';
    var finalPseudoElements = [];
    for (var selector in message.pseudoElementSelectorToCSSMap) {
      minimizePseudoElementStyle(message, doc, selector, finalPseudoElements);
    }
  
    if (finalPseudoElements.length > 0) {
      message.html[message.pseudoElementPlaceHolderIndex] =
          `<style>${finalPseudoElements.join(' ')}</style>`;
    }
  
    if (message.rootStyleIndex) {
      minimizeStyle(
          message,
          doc,
          doc.documentElement,
          message.rootId,
          message.rootStyleIndex);
    }
  
    for (var id in message.idToStyleIndex) {
      var index = message.idToStyleIndex[id];
      var element = doc.getElementById(id);
      if (element) {
        minimizeStyle(message, doc, element, id, index);
      }
    }
    iframe.remove();
  }
docs: Removes all style attribute properties that are unneeded.
  
  @param {Object} message The message Object whose style attributes should be
  minimized.