Bug 1343678 - Use window context for `GeckoSessionTestRule.evaluateJS()` r=geckoview-reviewers,droeh

Differential Revision: https://phabricator.services.mozilla.com/D41289

--HG--
extra : moz-landing-system : lando

mobile/android/geckoview/src/androidTest/assets/web_extensions/test-support/test-support.js

@@ -12,7 +12,7 @@ window.addEventListener("pageshow", () => {
       try {
         // Using eval here is the whole point of this WebExtension so we can
         // safely ignore the eslint warning.
-        const response = eval(message.eval); // eslint-disable-line no-eval
+        const response = window.eval(message.eval); // eslint-disable-line no-eval
         sendResponse(message.id, response);
       } catch (ex) {
         sendSyncResponse(message.id, null, ex);