Update documentation of Performance.timing/navigation

Source/core/timing/Performance.idl

Index: Source/core/timing/Performance.idl
diff --git a/Source/core/timing/Performance.idl b/Source/core/timing/Performance.idl
index 6a8fab6b0030ec60e72d6f7d0230919d69f66bae..d5353157e389649275ce45dde6600bfcd2a79bb2 100644
--- a/Source/core/timing/Performance.idl
+++ b/Source/core/timing/Performance.idl
@@ -53,13 +53,9 @@ interface Performance : EventTarget {
     attribute EventHandler onwebkitresourcetimingbufferfull;
 
     // Navigation Timing
-    // http://www.w3.org/TR/navigation-timing/#sec-window.performance-attribute
-    // TODO(philipj): The Navigation Timing Rec. defines the (not partial)
-    // Performance interface, while https://w3c.github.io/navigation-timing/ has
-    // changed the interface in an incompatible way:
-    // https://github.com/w3c/navigation-timing/issues/22
-    [Measure] readonly attribute PerformanceTiming timing;
-    [Measure] readonly attribute PerformanceNavigation navigation;
+    // https://w3c.github.io/navigation-timing/#extensions-to-the-performance-interface
+    [SameObject, Measure] readonly attribute PerformanceTiming timing;
+    [SameObject, Measure] readonly attribute PerformanceNavigation navigation;
 
     // User Timing
     // https://w3c.github.io/user-timing/#extensions-performance-interface