Use swap-promise to improve first* paint times

third_party/WebKit/Source/core/paint/PaintTiming.h

 // Copyright 2015 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.
 
 #ifndef PaintTiming_h
 #define PaintTiming_h
 
 #include "core/dom/Document.h"
 #include "core/paint/FirstMeaningfulPaintDetector.h"
 #include "platform/Supplementable.h"
 #include "platform/heap/Handle.h"
 #include "platform/wtf/Noncopyable.h"
 
 namespace blink {
 
 class LocalFrame;
 
 // PaintTiming is responsible for tracking paint-related timings for a given
 // document.
 class CORE_EXPORT PaintTiming final
     : public GarbageCollectedFinalized<PaintTiming>,
       public Supplement<Document> {
   WTF_MAKE_NONCOPYABLE(PaintTiming);
   USING_GARBAGE_COLLECTED_MIXIN(PaintTiming);
 
  public:
   virtual ~PaintTiming() {}
 
+  enum class PaintEvent {
+    kFirstPaint,
+    kFirstContentfulPaint,
+    kFirstMeaningfulPaint
+  };
+
   static PaintTiming& From(Document&);
 
   // mark*() methods record the time for the given paint event, record a trace
   // event, and notify that paint timing has changed. These methods do nothing
   // (early return) if a time has already been recorded for the given paint
   // event.
   void MarkFirstPaint();
 
   // markFirstTextPaint, markFirstImagePaint, and markFirstContentfulPaint
   // will also record first paint if first paint hasn't been recorded yet.
@@ skipping 36 matching lines @@
   // firstMeaningfulPaint, this signal is available in real time, but it may be
   // an optimistic (i.e., too early) estimate.
   double FirstMeaningfulPaintCandidate() const {
     return first_meaningful_paint_candidate_;
   }
 
   FirstMeaningfulPaintDetector& GetFirstMeaningfulPaintDetector() {
     return *fmp_detector_;
   }
 
+  void ReportSwapTime(PaintEvent, bool did_swap, double timestamp);

[sunnyps, 2017/05/02 01:20:46]

nit: newline after ReportSwapTime

[panicker, 2017/05/02 21:21:36]

Done.

   DECLARE_VIRTUAL_TRACE();
 
  private:
   explicit PaintTiming(Document&);
   LocalFrame* GetFrame() const;
   void NotifyPaintTimingChanged();
 
   // set*() set the timing for the given paint event to the given timestamp
   // and record a trace event if the value is currently zero, but do not
   // notify that paint timing changed. These methods can be invoked from other
   // mark*() or set*() methods to make sure that first paint is marked as part
   // of marking first contentful paint, or that first contentful paint is
   // marked as part of marking first text/image paint, for example.
   void SetFirstPaint(double stamp);
 
   // setFirstContentfulPaint will also set first paint time if first paint
   // time has not yet been recorded.
   void SetFirstContentfulPaint(double stamp);
 
+  void RegisterNotifySwapTime(PaintEvent);
+
   double first_paint_ = 0.0;
+  double first_paint_swap_ = 0.0;
   double first_text_paint_ = 0.0;
   double first_image_paint_ = 0.0;
   double first_contentful_paint_ = 0.0;
+  double first_contentful_paint_swap_ = 0.0;
   double first_meaningful_paint_ = 0.0;
+  double first_meaningful_paint_swap_ = 0.0;
   double first_meaningful_paint_candidate_ = 0.0;
 
   Member<FirstMeaningfulPaintDetector> fmp_detector_;
 };
 
 }  // namespace blink
 
 #endif