Use a new Supplement constructor for Supplement<Document> (Part 1)

third_party/WebKit/Source/core/css/CSSTiming.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/CSSTiming.h"
 
 #include "core/paint/PaintTiming.h"
 
 namespace blink {
 
@@ skipping 13 matching lines @@
   if (!m_paintTiming->firstContentfulPaint())
     m_parseTimeBeforeFCP += seconds;
 }
 
 void CSSTiming::recordUpdateDuration(double seconds) {
   if (!m_paintTiming->firstContentfulPaint())
     m_updateTimeBeforeFCP += seconds;
 }
 
 DEFINE_TRACE(CSSTiming) {
-  visitor->trace(m_document);
   visitor->trace(m_paintTiming);
   Supplement<Document>::trace(visitor);
 }
 
 CSSTiming::CSSTiming(Document& document)
-    : m_document(document), m_paintTiming(PaintTiming::from(document)) {}
+    : Supplement<Document>(document),
+      m_paintTiming(PaintTiming::from(document)) {}
 
 }  // namespace blink