Assert some invariants in TextTrack

Source/core/html/track/TextTrack.cpp

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  * Copyright (C) 2011, 2012, 2013 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 270 matching lines @@
 void TextTrack::removeCue(TextTrackCue* cue, ExceptionState& exceptionState)
 {
     ASSERT(cue);
 
     // https://html.spec.whatwg.org/multipage/embedded-content.html#dom-texttrack-removecue
 
     // The removeCue(cue) method of TextTrack objects, when invoked, must run the following steps:
 
     // 1. If the given cue is not currently listed in the method's TextTrack
     // object's text track's text track list of cues, then throw a NotFoundError exception.
-    // 2. Remove cue from the method's TextTrack object's text track's text track list of cues.
-    if (cue->track() != this || !m_cues || !m_cues->remove(cue)) {
+    if (cue->track() != this) {
         exceptionState.throwDOMException(NotFoundError, "The specified cue is not listed in the TextTrack's list of cues.");
         return;
     }
 
+    // cue->track() == this implies that cue is in this track's list of cues,
+    // so this track should have a list of cues and the cue being removed
+    // should be in it.
+    ASSERT(m_cues);
+
+    // 2. Remove cue from the method's TextTrack object's text track's text track list of cues.
+    bool wasRemoved = m_cues->remove(cue);
+    ASSERT_UNUSED(wasRemoved, wasRemoved);
+
     // If the cue is active, a timeline needs to be available.
     ASSERT(!cue->isActive() || cueTimeline());
 
     cue->setTrack(0);
 
     if (cueTimeline())
         cueTimeline()->removeCue(this, cue);
 }
 
 VTTRegionList* TextTrack::ensureVTTRegionList()
@@ skipping 70 matching lines @@
 void TextTrack::cueWillChange(TextTrackCue* cue)
 {
     // The cue may need to be repositioned in the media element's interval tree, may need to
     // be re-rendered, etc, so remove it before the modification...
     if (cueTimeline())
         cueTimeline()->removeCue(this, cue);
 }
 
 void TextTrack::cueDidChange(TextTrackCue* cue)
 {
+    // This method is called through cue->track(), which should imply that this
+    // track has a list of cues.
+    ASSERT(m_cues && cue->track() == this);
+
     // Make sure the TextTrackCueList order is up-to-date.
     // FIXME: Only need to do this if the change was to any of the timestamps.
-    ensureTextTrackCueList()->updateCueIndex(cue);
+    m_cues->updateCueIndex(cue);
 
     // Since a call to cueDidChange is always preceded by a call to
     // cueWillChange, the cue should no longer be active when we reach this
     // point (since it was removed from the timeline in cueWillChange).
     ASSERT(!cue->isActive());
 
     if (m_mode == disabledKeyword())
         return;
 
     // ... and add it back again if the track is enabled.
@@ skipping 76 matching lines @@
 {
     visitor->trace(m_cues);
     visitor->trace(m_activeCues);
     visitor->trace(m_regions);
     visitor->trace(m_trackList);
     TrackBase::trace(visitor);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink