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

third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetector.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/paint/FirstMeaningfulPaintDetector.h"
 
 #include "core/css/FontFaceSet.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/paint/PaintTiming.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
@@ skipping 18 matching lines @@
 }
 
 FirstMeaningfulPaintDetector::FirstMeaningfulPaintDetector(
     PaintTiming* paintTiming)
     : m_paintTiming(paintTiming),
       m_networkStableTimer(
           this,
           &FirstMeaningfulPaintDetector::networkStableTimerFired) {}
 
 Document* FirstMeaningfulPaintDetector::document() {
-  return m_paintTiming->document();
+  return m_paintTiming->host();
 }
 
 // Computes "layout significance" (http://goo.gl/rytlPL) of a layout operation.
 // Significance of a layout is the number of layout objects newly added to the
 // layout tree, weighted by page height (before and after the layout).
 // A paint after the most significance layout during page load is reported as
 // First Meaningful Paint.
 void FirstMeaningfulPaintDetector::markNextPaintAsMeaningfulIfNeeded(
     const LayoutObjectCounter& counter,
     int contentsHeightBeforeLayout,
@@ skipping 72 matching lines @@
   if (m_provisionalFirstMeaningfulPaint)
     m_paintTiming->setFirstMeaningfulPaint(m_provisionalFirstMeaningfulPaint);
   m_state = Reported;
 }
 
 DEFINE_TRACE(FirstMeaningfulPaintDetector) {
   visitor->trace(m_paintTiming);
 }
 
 }  // namespace blink