(core) Fix problem with localStorage in some cross-origin embed situations

Summary:
- Handle the possibility that any access to localStorage causes error.
- Move getStorage() and getSessionStorage() safe functions to a separate file.
- Use these safe functions in more places.

Test Plan:
Added a test case, using a webdriver instance that blocks third-party cookies,
to enforce third-party restrictions. Added to gristUtil a way to override the
webdriver instance.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3719

test/nbrowser/gristUtils.ts

@@ -7,8 +7,8 @@ import * as fse from 'fs-extra';
 import escapeRegExp = require('lodash/escapeRegExp');
 import noop = require('lodash/noop');
 import startCase = require('lodash/startCase');
-import { assert, driver, error, Key, WebElement, WebElementPromise } from 'mocha-webdriver';
-import { stackWrapFunc, stackWrapOwnMethods } from 'mocha-webdriver';
+import { assert, driver as driverOrig, error, Key, WebElement, WebElementPromise } from 'mocha-webdriver';
+import { stackWrapFunc, stackWrapOwnMethods, WebDriver } from 'mocha-webdriver';
 import * as path from 'path';
 
 import { decodeUrl } from 'app/common/gristUrls';
@@ -32,6 +32,15 @@ import type { AssertionError } from 'assert';
 // Wrap in a namespace so that we can apply stackWrapOwnMethods to all the exports together.
 namespace gristUtils {
 
+// Allow overriding the global 'driver' to use in gristUtil.
+let driver: WebDriver;
+
+// Substitute a custom driver to use with gristUtils functions. Omit argument to restore to default.
+export function setDriver(customDriver: WebDriver = driverOrig) { driver = customDriver; }
+
+// Set the 'driver' to use here in before() callback, because driverOrig isn't set until then.
+before(() => setDriver());
+
 const homeUtil = new HomeUtil(testUtils.fixturesRoot, server);
 
 export const createNewDoc = homeUtil.createNewDoc.bind(homeUtil);