Keep track in the browser of which frames have onunload and onbeforeunload handlers.

third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 236 matching lines @@
   DOMWindowSet::iterator it = set.find(domWindow);
   if (it == set.end())
     return;
   set.removeAll(it);
   if (set.isEmpty()) {
     updateSuddenTerminationStatus(domWindow, false,
                                   LocalFrameClient::BeforeUnloadHandler);
   }
 }
 
-static bool allowsBeforeUnloadListeners(LocalDOMWindow* window) {
-  DCHECK(window);
-  LocalFrame* frame = window->frame();
-  if (!frame)
-    return false;
-  return frame->isMainFrame();
-}
-
 unsigned LocalDOMWindow::pendingUnloadEventListeners() const {
   return windowsWithUnloadEventListeners().count(
       const_cast<LocalDOMWindow*>(this));
 }
 
 bool LocalDOMWindow::allowPopUp(LocalFrame& firstFrame) {
   if (UserGestureIndicator::utilizeUserGesture())
     return true;
 
   Settings* settings = firstFrame.settings();
@@ skipping 1151 matching lines @@
 
   for (auto& it : m_eventListenerObservers) {
     it->didAddEventListener(this, eventType);
   }
 
   if (eventType == EventTypeNames::unload) {
     UseCounter::count(document(), UseCounter::DocumentUnloadRegistered);
     addUnloadEventListener(this);
   } else if (eventType == EventTypeNames::beforeunload) {
     UseCounter::count(document(), UseCounter::DocumentBeforeUnloadRegistered);
-    if (allowsBeforeUnloadListeners(this)) {
-      // This is confusingly named. It doesn't actually add the listener. It
-      // just increments a count so that we know we have listeners registered
-      // for the purposes of determining if we can fast terminate the renderer
-      // process.

[dcheng, 2017/03/29 23:03:46]

Nit: please keep this comment.

[jam, 2017/03/30 14:53:23]

Done.

-      addBeforeUnloadEventListener(this);
-    } else {
-      // Subframes return false from allowsBeforeUnloadListeners.
+    addBeforeUnloadEventListener(this);
+    if (frame() && !frame()->isMainFrame())
       UseCounter::count(document(), UseCounter::SubFrameBeforeUnloadRegistered);
-    }
   }
 }
 
 void LocalDOMWindow::removedEventListener(
     const AtomicString& eventType,
     const RegisteredEventListener& registeredListener) {
   DOMWindow::removedEventListener(eventType, registeredListener);
   if (frame() && frame()->page())
     frame()->page()->eventHandlerRegistry().didRemoveEventHandler(
         *this, eventType, registeredListener.options());
 
   for (auto& it : m_eventListenerObservers) {
     it->didRemoveEventListener(this, eventType);
   }
 
   if (eventType == EventTypeNames::unload) {
     removeUnloadEventListener(this);
-  } else if (eventType == EventTypeNames::beforeunload &&
-             allowsBeforeUnloadListeners(this)) {
+  } else if (eventType == EventTypeNames::beforeunload) {
     removeBeforeUnloadEventListener(this);

[dcheng, 2017/03/29 23:03:46]

This would ideally be commented too.

[jam, 2017/03/30 14:53:23]

all 4 would need comment, to be consistent, or perhaps even better the method
name would be clearer. but since this existed before, I think it's orthogonal. 

   }
 }
 
 void LocalDOMWindow::warnUnusedPreloads(TimerBase* base) {
   if (frame() && frame()->loader().documentLoader()) {
     ResourceFetcher* fetcher = frame()->loader().documentLoader()->fetcher();
     DCHECK(fetcher);
     if (fetcher->countPreloads())
       fetcher->warnUnusedPreloads();
   }
@@ skipping 183 matching lines @@
   DOMWindow::trace(visitor);
   Supplementable<LocalDOMWindow>::trace(visitor);
 }
 
 DEFINE_TRACE_WRAPPERS(LocalDOMWindow) {
   visitor->traceWrappers(m_customElements);
   DOMWindow::traceWrappers(visitor);
 }
 
 }  // namespace blink