Have Node::document() return a reference instead of a pointer

Source/core/html/track/LoadableTextTrack.cpp

Index: Source/core/html/track/LoadableTextTrack.cpp
diff --git a/Source/core/html/track/LoadableTextTrack.cpp b/Source/core/html/track/LoadableTextTrack.cpp
index 51c9722250d328a03e0a5c9f0037944a75827b02..9ccb64b53af3cd7ff940c116f49877a865306d9d 100644
--- a/Source/core/html/track/LoadableTextTrack.cpp
+++ b/Source/core/html/track/LoadableTextTrack.cpp
@@ -34,7 +34,7 @@
 namespace WebCore {
 
 LoadableTextTrack::LoadableTextTrack(HTMLTrackElement* track, const String& kind, const String& label, const String& language)
-    : TextTrack(track->document(), track, kind, label, language, TrackElement)
+    : TextTrack(&track->document(), track, kind, label, language, TrackElement)
     , m_trackElement(track)
     , m_loadTimer(this, &LoadableTextTrack::loadTimerFired)
     , m_isDefault(false)
@@ -89,7 +89,7 @@ void LoadableTextTrack::loadTimerFired(Timer<LoadableTextTrack>*)
     // 4. Download: If URL is not the empty string, perform a potentially CORS-enabled fetch of URL, with the
     // mode being the state of the media element's crossorigin content attribute, the origin being the
     // origin of the media element's Document, and the default origin behaviour set to fail.
-    m_loader = TextTrackLoader::create(this, static_cast<ScriptExecutionContext*>(m_trackElement->document()));
+    m_loader = TextTrackLoader::create(this, static_cast<ScriptExecutionContext*>(&m_trackElement->document()));
     if (!m_loader->load(m_url, m_trackElement->mediaElementCrossOriginAttribute()))
         m_trackElement->didCompleteLoad(this, HTMLTrackElement::Failure);
 }