Followup comments from r460581.

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

Index: third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
diff --git a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
index cae0bb12134adec74ada3184674c5fb56990de92..72352ee3abe470d628d8b274c022d7eaeac3d209 100644
--- a/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
+++ b/third_party/WebKit/Source/core/frame/LocalDOMWindow.cpp
@@ -1425,6 +1425,10 @@ void LocalDOMWindow::addedEventListener(
     addUnloadEventListener(this);
   } else if (eventType == EventTypeNames::beforeunload) {
     UseCounter::count(document(), UseCounter::DocumentBeforeUnloadRegistered);
+    // 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, 2017/03/30 19:16:57]

Nit: move this to line 1423 (since it applies equally to addUnloadEventListener
as well)

     addBeforeUnloadEventListener(this);
     if (frame() && !frame()->isMainFrame())
       UseCounter::count(document(), UseCounter::SubFrameBeforeUnloadRegistered);