Use swap-promise to improve first* paint times

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

Index: third_party/WebKit/Source/core/paint/PaintTiming.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintTiming.cpp b/third_party/WebKit/Source/core/paint/PaintTiming.cpp
index fae6893ff847960b441603f6225449b779476646..754646ef012db230cf2eabbc0284ee5027f61c34 100644
--- a/third_party/WebKit/Source/core/paint/PaintTiming.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintTiming.cpp
@@ -9,10 +9,13 @@
 #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 {
 
@@ -100,6 +103,7 @@ void PaintTiming::SetFirstMeaningfulPaint(double stamp) {
       TraceEvent::ToTraceTimestamp(first_meaningful_paint_), "frame",
       GetFrame());
   NotifyPaintTimingChanged();
+  RegisterNotifySwapTime(PaintEvent::kFirstMeaningfulPaint);
 }
 
 void PaintTiming::NotifyPaint(bool is_first_paint,
@@ -142,6 +146,7 @@ void PaintTiming::SetFirstPaint(double stamp) {
 
   TRACE_EVENT_INSTANT1("loading,rail,devtools.timeline", "firstPaint",
                        TRACE_EVENT_SCOPE_PROCESS, "frame", GetFrame());
+  RegisterNotifySwapTime(PaintEvent::kFirstPaint);
 }
 
 void PaintTiming::SetFirstContentfulPaint(double stamp) {
@@ -152,8 +157,42 @@ void PaintTiming::SetFirstContentfulPaint(double 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