Add a counter and a deprecation message when navigating in an unload handler.

third_party/WebKit/Source/core/loader/FrameLoader.cpp

Index: third_party/WebKit/Source/core/loader/FrameLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/FrameLoader.cpp b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
index da7e510ebd2a3daab476a994525e08db3564450d..0560c561b9cfaa5642edbfb9560ca624d1023dac 100644
--- a/third_party/WebKit/Source/core/loader/FrameLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
@@ -258,6 +258,8 @@ void FrameLoader::saveScrollState()
 
 void FrameLoader::dispatchUnloadEvent()
 {
+    NavigationCounterForUnload counter;
+
     // If the frame is unloading, the provisional loader should no longer be
     // protected. It will be detached soon.
     m_protectProvisionalLoader = false;