Use event init dictionary in core/html/track

Source/core/html/track/TrackEvent.cpp

 /*
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 15 matching lines @@
 #include "config.h"
 #include "core/html/track/TrackEvent.h"
 
 #include "bindings/core/v8/UnionTypesCore.h"
 #include "core/html/track/AudioTrack.h"
 #include "core/html/track/TextTrack.h"
 #include "core/html/track/VideoTrack.h"
 
 namespace blink {
 
-TrackEventInit::TrackEventInit()
-{
-}
-
-
 TrackEvent::TrackEvent()
 {
 }
 
 TrackEvent::TrackEvent(const AtomicString& type, const TrackEventInit& initializer)
     : Event(type, initializer)
-    , m_track(initializer.track)
 {
+    const VideoTrackOrAudioTrackOrTextTrack& track = initializer.track();
+    if (track.isVideoTrack())
+        m_track = track.getAsVideoTrack();
+    if (track.isAudioTrack())

[philipj_slow, 2014/12/10 08:22:48]

I'm guessing the compiler can't figure out that these are mutually exclusive by
itself, so use else if here and add ASSERT_UNREACHED at the end?

[bashi, 2014/12/10 08:45:56]

Done. The compiler checks the type of the given value, but it can't figure out
they are subclass of TrackBase, so these conditions are needed.

...And I should have checked hasTrack() before using track().

+        m_track = track.getAsAudioTrack();
+    if (track.isTextTrack())
+        m_track = track.getAsTextTrack();
 }
 
 TrackEvent::~TrackEvent()
 {
 }
 
 const AtomicString& TrackEvent::interfaceName() const
 {
     return EventNames::TrackEvent;
 }
@@ skipping 19 matching lines @@
 }
 
 void TrackEvent::trace(Visitor* visitor)
 {
     visitor->trace(m_track);
     Event::trace(visitor);
 }
 
 } // namespace blink