code: function outputHTMLString(messages) {
    var rootIndex = 0;
    for (var i = 1; i < messages.length; i++) {
      rootIndex = messages[i].frameIndex === '0' ? i : rootIndex;
    }
    fillRemainingHolesAndMinimizeStyles(messages, rootIndex);
    return messages[rootIndex].html.join('');
  }
docs: Converts the responses from the injected content scripts into a string
  representing the HTML.
  
  @param {Array<Object>} messages The response from all of the injected content
  scripts.
  @return {string} The resulting HTML.