Bug 1727653 - wait for resize event before testing restoration of persisted...

Bug 1727653 - wait for resize event before testing restoration of persisted sizes. r=niklas, a=RyanVM

Differential Revision: https://phabricator.services.mozilla.com/D149329

toolkit/content/tests/chrome/test_navigate_persist.html

@@ -25,15 +25,22 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1460639
       });
     }
 
-    function resize(win, size) {
-      let resizePromise = new Promise(resolve => {
-        if (win.outerWidth === size && win.outerHeight === size) {
+    function promiseMaybeResizeEvent(win, expectedSize) {
+      return new Promise(resolve => {
+        // If the size is already as expected, then there may be no resize
+        // event.
+        if (win.outerWidth === expectedSize
+            && win.outerHeight === expectedSize) {
           resolve();
         }
         win.addEventListener("resize", () => {
           resolve();
         }, {once: true});
       });
+    }
+
+    function resize(win, size) {
+      const resizePromise = promiseMaybeResizeEvent(win, size);
       win.resizeTo(size, size);
       return resizePromise;
     }
@@ -60,6 +67,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1460639
       isnot(win.outerHeight, PERSIST_SIZE, "Initial window height is not the persisted size");
 
       await navigateWindowTo(win, "window_navigate_persist.html");
+      await promiseMaybeResizeEvent(win, PERSIST_SIZE);
       is(win.outerWidth, PERSIST_SIZE, "Window width is persisted");
       is(win.outerHeight, PERSIST_SIZE, "Window height is persisted");
       win.close();