Bug 1678813 - part1 : use `waitForFocus()` to ensure the window is focus before entering fullscreen. r=bryce

This patch will revert the change from D87540 and D98014, so the orginal problem of causing intermittent failure is that current method we use can't garantees that the window is already focused before calling fullscreen API, which results in a rejected fullscreen request.

Therefore, using another method `waitForFocus()` to ensure that. From the try server result, this method is more stable than our previous method which is checking the document visibility.

Differential Revision: https://phabricator.services.mozilla.com/D98282

dom/media/mediacontrol/tests/browser/browser_nosrc_and_error_media.js

@@ -33,18 +33,18 @@ add_task(async function testNoSrcOrErrorMediaEntersPIPMode() {
       ok(false, "should not get activated!");
     };
 
-    info(`enter and leave PIP mode which would not affect controller`);
+    info(`enter PIP mode which would not affect controller`);
     const winPIP = await triggerPictureInPicture(
       tab.linkedBrowser,
       testVideoId
     );
-    await Promise.all([
-      // To ensure the focus would be gave back to the original window. If we do
-      // not do that, then lacking of focus would interfere other following tests.
-      SimpleTest.promiseFocus(window),
-      ensureMessageAndClosePiP(tab.linkedBrowser, testVideoId, winPIP, false),
-    ]);
-
+    info(`leave PIP mode`);
+    await ensureMessageAndClosePiP(
+      tab.linkedBrowser,
+      testVideoId,
+      winPIP,
+      false
+    );
     ok(!controller.isActive, "controller is still inactive");
 
     info(`remove tab`);
@@ -64,7 +64,6 @@ add_task(async function testNoSrcOrErrorMediaEntersFullscreen() {
     };
 
     info(`enter and leave fullscreen which would not affect controller`);
-    await ensureTabIsAlreadyFocused(tab);
     await enterAndLeaveFullScreen(tab, testVideoId);
     ok(!controller.isActive, "controller is still inactive");
 
@@ -76,26 +75,11 @@ add_task(async function testNoSrcOrErrorMediaEntersFullscreen() {
 /**
  * The following is helper function.
  */
-function ensureTabIsAlreadyFocused(tab) {
-  return SpecialPowers.spawn(tab.linkedBrowser, [], () => {
-    // fullscreen can only be request from a visible tab, sometime we excecute
-    // this method too early where the tab hasn't become a focus tab.
-    if (content.document.visibilityState != "visible") {
-      info(`wait until tab becomes a focus tab`);
-      return new Promise(r => {
-        content.document.onvisibilitychange = () => {
-          if (content.document.visibilityState == "visible") {
-            r();
-          }
-        };
-      });
-    }
-    return Promise.resolve();
-  });
-}
-
-function enterAndLeaveFullScreen(tab, elementId) {
-  return SpecialPowers.spawn(tab.linkedBrowser, [elementId], elementId => {
+async function enterAndLeaveFullScreen(tab, elementId) {
+  await new Promise(resolve =>
+    SimpleTest.waitForFocus(resolve, tab.linkedBrowser.ownerGlobal)
+  );
+  await SpecialPowers.spawn(tab.linkedBrowser, [elementId], elementId => {
     return new Promise(r => {
       const element = content.document.getElementById(elementId);
       ok(!content.document.fullscreenElement, "no fullscreen element");