[Camp_GA] JS issue when cookies are disabled

[FrClem]

Viewed on: 2018-03-27
URL to reproduce: https://secure.mencap.org.uk
Browser: Chrom(ium) 64 on Linux, Cookies DISABLED

Inspector error:

Uncaught DOMException: Failed to read the 'sessionStorage' property from 'Window': Access is denied for this document.
at Object.Drupal.behaviors.campaignion_google_analytics_donation.attach

Related JS code, in particular:

if (typeof window.sessionStorage === 'undefined') {
        window.sessionStorage = {};
        window.sessionStorage['setItem'] = function () {};
        window.sessionStorage['getItem'] = function () {};
        window.sessionStorage['removeItem'] = function () {};
      }

window.sessionStorage cannot be read => JS error ==> page looks weird

moreonion/morelesszen#1 might be a related issue