Add stubbed sessionStorage object.

Author: kirk-sayre-work

boilerplate.js

@@ -1223,6 +1223,10 @@ var exports = {};
 function fetch(url, data) {
  lib.logIOC("fetch", {url: url, data: data}, "The script fetch()ed a URL.");
  lib.logUrl("fetch", url);
+ return {
+ok : true,
+json : function() { return "1"; },
+ };
 };
 
 // Image class stub.
@@ -1317,3 +1321,8 @@ var history = {
  pushState: function() {},
 };
 
+// Fake sessionStorage object.
+var sessionStorage = {
+ getItem: function() {},
+ setItem: function() {},
+};