[FirstMeaningfulPaint] Do not stop observing layouts before FirstContentfulPaint

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/tracing/TraceEvent.h"
@@ skipping 97 matching lines @@
   DCHECK(document());
   if (m_state == Reported || document()->fetcher()->hasPendingRequest())
     return;
 
   m_networkStableTimer.startOneShot(kSecondsWithoutNetworkActivityThreshold,
                                     BLINK_FROM_HERE);
 }
 
 void FirstMeaningfulPaintDetector::networkStableTimerFired(TimerBase*) {
   if (m_state == Reported || !document() ||
-      document()->fetcher()->hasPendingRequest())
+      document()->fetcher()->hasPendingRequest() ||
+      !m_paintTiming->firstContentfulPaint())
     return;
 
   if (m_provisionalFirstMeaningfulPaint)
     m_paintTiming->setFirstMeaningfulPaint(m_provisionalFirstMeaningfulPaint);
   m_state = Reported;
 }
 
 DEFINE_TRACE(FirstMeaningfulPaintDetector) {
   visitor->trace(m_paintTiming);
 }
 
 }  // namespace blink