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 488b56fde73ee5b26389ad709c2336551e1f5490..f529401d9f5aa8a14cf538c9e232075b78b35d36 100644
--- a/third_party/WebKit/Source/core/loader/FrameLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameLoader.cpp
@@ -1087,6 +1087,8 @@ bool FrameLoader::prepareForCommit()
     SubframeLoadingDisabler disabler(m_frame->document());
     if (m_documentLoader) {
         client()->dispatchWillClose();
+
+        NavigationCounterForUnload counter;

[Nate Chapin, 2016/05/13 21:56:10]

Is there any reason not to put this in dispatchUnloadEvent()?

[lfg, 2016/05/14 01:23:28]

The only reason is because I didn't want to fire the deprecation warning in
cases where we already block the navigations (scheduled navigations get
cancelled here:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...).

[Nate Chapin, 2016/05/16 21:00:31]

Right, only same-document navigations can run and complete here. But
dispatchUnloadEvent() is also called in other places for frame detach, page
close, and swap out, and the unload event could certainly do a same-document
navigation from there. Is it intentional to exclude those cases from the
counter?

[lfg, 2016/05/16 23:46:54]

Ah, good point. Yes, we should count those cases as well, I've moved the code to
dispatchUnloadEvent().

         dispatchUnloadEvent();
     }
     m_frame->detachChildren();