Report nav timing 2 instance as soon as it's requested.

third_party/WebKit/Source/core/timing/Performance.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 25 matching lines @@
 #include "core/dom/Document.h"
 #include "core/dom/QualifiedName.h"
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/frame/DOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/UseCounter.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/loader/DocumentLoader.h"
 #include "core/origin_trials/OriginTrials.h"
 #include "core/timing/PerformanceTiming.h"
+#include "platform/network/ResourceTimingInfo.h"
 
 static const double kLongTaskThreshold = 0.05;
 
 static const char kUnknownAttribution[] = "unknown";
 static const char kAmbiguousAttribution[] = "multiple-contexts";
 static const char kSameOriginAttribution[] = "same-origin";
 static const char kSameOriginSelfAttribution[] = "self";
 static const char kSameOriginAncestorAttribution[] = "same-origin-ancestor";
 static const char kSameOriginDescendantAttribution[] = "same-origin-descendant";
 static const char kCrossOriginAncestorAttribution[] = "cross-origin-ancestor";
@@ skipping 77 matching lines @@
   return m_navigation.get();
 }
 
 PerformanceTiming* Performance::timing() const {
   if (!m_timing)
     m_timing = PerformanceTiming::create(frame());
 
   return m_timing.get();
 }
 
+PerformanceNavigationTiming* Performance::createNavigationTimingInstance() {
+  ResourceTimingInfo* resourceTimingInfo = nullptr;
+  if (frame()) {

[Kunihiko Sakamoto, 2017/02/15 06:35:30]

If frame() is null, can we return nullptr here? Currently we're returning
PerformanceNavigationTiming(nullptr, nullptr, timeOrigin()), which isn't useful
at all.

Then we can get rid of many null checks in PerformanceNavigationTiming.

[sunjian, 2017/02/15 20:30:28]

Agree with returning nullptr directly when frame() is nullptr. Not sur e we
can't get rid of null checks in PerformanceNavigationTiming. Because even though
PerformanceNavigationTiming can be constructed with a non-null frame, it might
become nullptr halfway right? LocalFrame is only a WeakMember of
PerformanceNavigationTiming.

[panicker, 2017/02/16 00:37:23]

Which dchecks are being referred to here specifically?

[Kunihiko Sakamoto, 2017/02/16 08:42:29]

Ah I overlooked that m_frame is a weak pointer.

Similarly, can we return a nullptr if documentLoader->getNavigationTimingInfo()
is null?

[sunjian, 2017/02/16 22:30:49]

Acknowledged.

+    const DocumentLoader* documentLoader = frame()->loader().documentLoader();
+    DCHECK(documentLoader);
+    resourceTimingInfo = documentLoader->getNavigationTimingInfo();
+  }
+
+  return new PerformanceNavigationTiming(frame(), resourceTimingInfo,
+                                         timeOrigin());
+}
+
 void Performance::updateLongTaskInstrumentation() {
   DCHECK(frame());
   if (!frame()->document())
     return;
 
   if (hasObserverFor(PerformanceEntry::LongTask)) {
     UseCounter::count(frame()->localFrameRoot(), UseCounter::LongTaskObserver);
     frame()->performanceMonitor()->subscribe(PerformanceMonitor::kLongTask,
                                              kLongTaskThreshold, this);
   } else {
@@ skipping 91 matching lines @@
     HTMLFrameOwnerElement* frameOwner =
         culpritDomWindow->frame()->deprecatedLocalOwner();
     addLongTaskTiming(startTime, endTime, attribution.first,
                       getFrameAttribute(frameOwner, HTMLNames::srcAttr, false),
                       getFrameAttribute(frameOwner, HTMLNames::idAttr, false),
                       getFrameAttribute(frameOwner, HTMLNames::nameAttr, true));
   }
 }
 
 }  // namespace blink