Move isNavigationAllowed() check to main entry point for loads.

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

Index: third_party/WebKit/Source/core/loader/NavigationScheduler.cpp
diff --git a/third_party/WebKit/Source/core/loader/NavigationScheduler.cpp b/third_party/WebKit/Source/core/loader/NavigationScheduler.cpp
index b33d21493967ed0059abfd29dba13408abff5137..ee3d96e63f8eecd90b088226dc2976179a52ac91 100644
--- a/third_party/WebKit/Source/core/loader/NavigationScheduler.cpp
+++ b/third_party/WebKit/Source/core/loader/NavigationScheduler.cpp
@@ -278,6 +278,21 @@ bool NavigationScheduler::isNavigationScheduledWithin(double interval) const
     return m_redirect && m_redirect->delay() <= interval;
 }
 
+// TODO(dcheng): There are really two different load blocking concepts at work here and they have
+// been incorrectly tangled together.
+//
+// 1. NavigationDisablerForBeforeUnload is for blocking navigation scheduling during a beforeunload
+//    event. Scheduled navigations during beforeunload would make it possible to get trapped in an
+//    endless loop of beforeunload dialogs.
+//
+//    Checking Frame::isNavigationAllowed() doesn't make sense in this context: NavigationScheduler
+//    is always cleared when a new load commits, so it's impossible for a scheduled navigation to
+//    clobber a navigation that just committed.
+//
+// 2. FrameNavigationDisabler / LocalFrame::isNavigationAllowed() is intended to prevent Documents
+//    from being reattached during destruction, since it can cause bugs with security origin
+//    confusion. This is primarily intended to block /synchronous/ navigations during things lke
+//    Document::detach().
 inline bool NavigationScheduler::shouldScheduleReload() const
 {
     return m_frame->page() && m_frame->isNavigationAllowed() && NavigationDisablerForBeforeUnload::isNavigationAllowed();