Ensure the scheduler always changes from UseCase LOADING to NONE.

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/dom/TaskRunnerHelper.h"
 #include "core/paint/PaintTiming.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
@@ skipping 86 matching lines @@
   TRACE_EVENT_MARK_WITH_TIMESTAMP1(
       "loading", "firstMeaningfulPaintCandidate",
       TraceEvent::toTraceTimestamp(m_provisionalFirstMeaningfulPaint), "frame",
       document()->frame());
   // Ignore the first meaningful paint candidate as this generally is the first
   // contentful paint itself.
   if (!m_seenFirstMeaningfulPaintCandidate) {
     m_seenFirstMeaningfulPaintCandidate = true;
     return;
   }
-  m_paintTiming->markFirstMeaningfulPaintCandidate();
+  m_paintTiming->markFirstMeaningfulPaintCandidate(
+      m_provisionalFirstMeaningfulPaint);
 }
 
 void FirstMeaningfulPaintDetector::checkNetworkStable() {
   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() ||
       !m_paintTiming->firstContentfulPaint())
     return;
 
   if (m_provisionalFirstMeaningfulPaint) {
+    // If there's only been one contentful paint, then there won't have been
+    // a meaningful paint signalled to the Scheduler, so mark one now.
+    // This is a no-op if a FMPC has already been marked.
+    m_paintTiming->markFirstMeaningfulPaintCandidate(
+        m_provisionalFirstMeaningfulPaint);
     // Enforce FirstContentfulPaint <= FirstMeaningfulPaint.
     double timestamp = std::max(m_provisionalFirstMeaningfulPaint,
                                 m_paintTiming->firstContentfulPaint());
     m_paintTiming->setFirstMeaningfulPaint(timestamp);
   }
   m_state = Reported;
 }
 
 DEFINE_TRACE(FirstMeaningfulPaintDetector) {
   visitor->trace(m_paintTiming);
 }
 
 }  // namespace blink