Use swap-promise to improve first* paint times

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

 // 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.
 
 #include "core/paint/PaintTiming.h"
 
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalDOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/loader/DocumentLoader.h"
+#include "core/page/ChromeClient.h"
+#include "core/page/Page.h"
 #include "core/timing/DOMWindowPerformance.h"
 #include "core/timing/Performance.h"
 #include "platform/WebFrameScheduler.h"
 #include "platform/instrumentation/tracing/TraceEvent.h"
+#include "public/platform/WebLayerTreeView.h"
 
 namespace blink {
 
 namespace {
 
 Performance* GetPerformanceInstance(LocalFrame* frame) {
   Performance* performance = nullptr;
   if (frame && frame->DomWindow()) {
     performance = DOMWindowPerformance::performance(*frame->DomWindow());
   }
@@ skipping 67 matching lines @@
 }
 
 void PaintTiming::SetFirstMeaningfulPaint(double stamp) {
   DCHECK_EQ(first_meaningful_paint_, 0.0);
   first_meaningful_paint_ = stamp;
   TRACE_EVENT_MARK_WITH_TIMESTAMP1(
       "loading,rail,devtools.timeline", "firstMeaningfulPaint",
       TraceEvent::ToTraceTimestamp(first_meaningful_paint_), "frame",
       GetFrame());
   NotifyPaintTimingChanged();
+  RegisterNotifySwapTime(PaintEvent::kFirstMeaningfulPaint);
 }
 
 void PaintTiming::NotifyPaint(bool is_first_paint,
                               bool text_painted,
                               bool image_painted) {
   if (is_first_paint)
     MarkFirstPaint();
   if (text_painted)
     MarkFirstTextPaint();
   if (image_painted)
@@ skipping 22 matching lines @@
 void PaintTiming::SetFirstPaint(double stamp) {
   if (first_paint_ != 0.0)
     return;
   first_paint_ = stamp;
   Performance* performance = GetPerformanceInstance(GetFrame());
   if (performance)
     performance->AddFirstPaintTiming(first_paint_);
 
   TRACE_EVENT_INSTANT1("loading,rail,devtools.timeline", "firstPaint",
                        TRACE_EVENT_SCOPE_PROCESS, "frame", GetFrame());
+  RegisterNotifySwapTime(PaintEvent::kFirstPaint);
 }
 
 void PaintTiming::SetFirstContentfulPaint(double stamp) {
   if (first_contentful_paint_ != 0.0)
     return;
   SetFirstPaint(stamp);
   first_contentful_paint_ = stamp;
   Performance* performance = GetPerformanceInstance(GetFrame());
   if (performance)
     performance->AddFirstContentfulPaintTiming(first_contentful_paint_);
+
   TRACE_EVENT_INSTANT1("loading,rail,devtools.timeline", "firstContentfulPaint",
                        TRACE_EVENT_SCOPE_PROCESS, "frame", GetFrame());
+  RegisterNotifySwapTime(PaintEvent::kFirstContentfulPaint);
+}
+
+void PaintTiming::RegisterNotifySwapTime(PaintEvent event) {
+  // ReportSwapTime on layerTreeView will queue a swap-promise, the callback is
+  // called when the swap for current render frame completes or fails to happen.
+  if (GetFrame()->GetPage() &&

[enne (OOO), 2017/05/01 21:58:11]

style nit: could rewrite this as "if (!GetPage) return;" and then if (WLTV*
layerTreeView = super long indirection) and not have to repeat the
Get->Get->Get->Get->Get part.

[panicker, 2017/05/02 00:57:04]

Done.

+      GetFrame()->GetPage()->GetChromeClient().GetWebLayerTreeView(
+          GetFrame())) {
+    WebLayerTreeView* layerTreeView =
+        GetFrame()->GetPage()->GetChromeClient().GetWebLayerTreeView(
+            GetFrame());
+    layerTreeView->NotifySwapTime(ConvertToBaseCallback(WTF::Bind(
+        &PaintTiming::ReportSwapTime, WrapWeakPersistent(this), event)));
+  }
+}
+
+void PaintTiming::ReportSwapTime(PaintEvent event,
+                                 bool did_swap,
+                                 double timestamp) {
+  if (did_swap) {

[enne (OOO), 2017/05/01 21:58:11]

style nit: could early out here instead of indenting everything

[panicker, 2017/05/02 00:57:04]

Done.

+    switch (event) {
+      case PaintEvent::kFirstPaint:
+        first_paint_swap_ = timestamp;
+        break;
+      case PaintEvent::kFirstContentfulPaint:
+        first_contentful_paint_swap_ = timestamp;
+        break;
+      case PaintEvent::kFirstMeaningfulPaint:
+        first_meaningful_paint_swap_ = timestamp;
+        break;
+    }
+  }
 }
 
 }  // namespace blink