Bug 1530179: Replace promiseWaitForCondition with TestUtils.waitForCondition in browser_double_close_tab.js r=johannh

Changed promiseWaitForCondition in line 69 to TestUtils.waitForCondition

Differential Revision: https://phabricator.services.mozilla.com/D21875

--HG--
extra : source : b6c437beca6240f394f7d0c7d5631278f64b499d

browser/base/content/test/general/browser_double_close_tab.js

@@ -66,7 +66,7 @@ add_task(async function() {
     // Click once:
     document.getAnonymousElementByAttribute(testTab, "anonid", "close-button").click();
   });
-  await promiseWaitForCondition(() => !testTab.parentNode);
+  await TestUtils.waitForCondition(() => !testTab.parentNode);
   ok(!testTab.parentNode, "Tab should be closed completely");
 });