Bug 1530585 - Re-enable test_background_video_resume_after_end_show_last_frame.html r=jya

The test expects that video is visible. The test needs to wait until the video element becomes visible. And appending a video element to document with loading the test video triggered 'mozentervideosuspend' event. It caused the test failure.

Differential Revision: https://phabricator.services.mozilla.com/D21174

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

dom/media/test/mochitest.ini

@@ -1284,7 +1284,7 @@ tags = suspend
 skip-if = toolkit == 'android' # bug 1346705
 tags = suspend
 [test_background_video_resume_after_end_show_last_frame.html]
-skip-if = toolkit == 'android' || ( webrender && os == "linux") # bug 1346705, bug 1516043
+skip-if = toolkit == 'android' # bug 1346705
 tags = suspend
 [test_background_video_suspend.html]
 skip-if = toolkit == 'android' # android(bug 1304480)

dom/media/test/test_background_video_resume_after_end_show_last_frame.html

@@ -101,7 +101,7 @@ startTest({
   tests: gDecodeSuspendTests,
 
   runTest: (test, token) => {
-    let v = appendVideoToDoc(test.name, token);
+    let v = appendVideoToDocWithoutLoad(token);
     let vReference = appendVideoToDocWithoutLoad(token+"-ref");
     manager.started(token);
 
@@ -110,7 +110,11 @@ startTest({
      * resuming video decoder should seek to the last frame.
      * This issue was found in bug 1358057.
      */
-    Promise.all([waitUntilPlaying(v), loadAndWaitUntilLoadedmetadata(vReference, test.name, "auto")])
+    waitUntilVisible(v)
+      .then(() => {
+        return Promise.all([loadAndWaitUntilLoadedmetadata(v, test.name), loadAndWaitUntilLoadedmetadata(vReference, test.name, "auto")]);
+      })
+      .then(() => waitUntilPlaying(v))
       .then(() => testVideoSuspendsWhenHidden(v))
       .then(() => {
         return Promise.all([waitUntilEnded(v), waitUntilSeekToLastFrame(vReference)]);