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

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

Index: third_party/WebKit/Source/core/timing/Performance.cpp
diff --git a/third_party/WebKit/Source/core/timing/Performance.cpp b/third_party/WebKit/Source/core/timing/Performance.cpp
index 20e24d20693b5bd6a4eb7f10a0cc1b28e6d5309b..16c5de7eabbc00feb223ffed1d8f8181bf9b6d9a 100644
--- a/third_party/WebKit/Source/core/timing/Performance.cpp
+++ b/third_party/WebKit/Source/core/timing/Performance.cpp
@@ -43,6 +43,7 @@
 #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;
 
@@ -140,6 +141,18 @@ PerformanceTiming* Performance::timing() const {
   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())