Bug 1548923 - part2 : reset cues' active flag when media element's ready state becomes 'HAVE_NOTHING' r=jya

According to the spec [1], whenever the media element's readyState is changed back to `HAVE_NOTHING`, we have to reset all cues' active flag and update cue display in order to hide them.

[1] https://html.spec.whatwg.org/multipage/media.html#text-track-cue-active-flag

Differential Revision: https://phabricator.services.mozilla.com/D30110

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

dom/html/HTMLMediaElement.cpp

@@ -1875,10 +1875,6 @@ void HTMLMediaElement::AbortExistingLoads() {
 
   mIsRunningSelectResource = false;
 
-  if (mTextTrackManager) {
-    mTextTrackManager->NotifyReset();
-  }
-
   mEventDeliveryPaused = false;
   mPendingEvents.Clear();
   mCurrentLoadPlayTime.Reset();
@@ -5521,6 +5517,13 @@ void HTMLMediaElement::ChangeReadyState(nsMediaReadyState aState) {
 
   DDLOG(DDLogCategory::Property, "ready_state", gReadyStateToString[aState]);
 
+  // https://html.spec.whatwg.org/multipage/media.html#text-track-cue-active-flag
+  // The user agent must synchronously unset cues' active flag whenever the
+  // media element's readyState is changed back to HAVE_NOTHING.
+  if (mReadyState == HAVE_NOTHING && mTextTrackManager) {
+    mTextTrackManager->NotifyReset();
+  }
+
   if (mNetworkState == NETWORK_EMPTY) {
     return;
   }

dom/html/TextTrackManager.cpp

@@ -824,8 +824,14 @@ void TextTrackManager::NotifyCueUpdated(TextTrackCue* aCue) {
 }
 
 void TextTrackManager::NotifyReset() {
+  // https://html.spec.whatwg.org/multipage/media.html#text-track-cue-active-flag
+  // This will unset all cues' active flag and update the cue display.
   WEBVTT_LOG("NotifyReset");
   mLastTimeMarchesOnCalled = media::TimeUnit::Zero();
+  for (uint32_t idx = 0; idx < mTextTracks->Length(); ++idx) {
+    (*mTextTracks)[idx]->SetCuesInactive();
+  }
+  UpdateCueDisplay();
 }
 
 void TextTrackManager::ReportTelemetryForTrack(TextTrack* aTextTrack) const {

dom/media/TextTrack.cpp

@@ -222,7 +222,10 @@ void TextTrack::SetTrackElement(HTMLTrackElement* aTrackElement) {
   mTrackElement = aTrackElement;
 }
 
-void TextTrack::SetCuesInactive() { mCueList->SetCuesInactive(); }
+void TextTrack::SetCuesInactive() {
+  WEBVTT_LOG("SetCuesInactive");
+  mCueList->SetCuesInactive();
+}
 
 void TextTrack::NotifyCueUpdated(TextTrackCue* aCue) {
   WEBVTT_LOG("NotifyCueUpdated, cue=%p", aCue);