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

third_party/WebKit/Source/core/timing/PerformanceEntry.h

Index: third_party/WebKit/Source/core/timing/PerformanceEntry.h
diff --git a/third_party/WebKit/Source/core/timing/PerformanceEntry.h b/third_party/WebKit/Source/core/timing/PerformanceEntry.h
index e3b75748617f6286a07b57ba6b46d3d9cbec66a3..d93b0124130ba787d03b1e9c03d15630275a4905 100644
--- a/third_party/WebKit/Source/core/timing/PerformanceEntry.h
+++ b/third_party/WebKit/Source/core/timing/PerformanceEntry.h
@@ -71,7 +71,11 @@ class CORE_EXPORT PerformanceEntry
   String name() const;
   String entryType() const;
   DOMHighResTimeStamp startTime() const;
-  DOMHighResTimeStamp duration() const;
+  // PerformanceNavigationTiming will override this due to
+  // the nature of reporting it early, which means not having a
+  // finish time available at construction time.
+  // Other classes must NOT override this.
+  virtual DOMHighResTimeStamp duration() const;
 
   ScriptValue toJSONForBinding(ScriptState*) const;