Allow navigations to frames that aren't being unloaded in the unload handler.

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

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  *
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 121 matching lines @@
 void History::go(ExecutionContext* context, int delta) {
   if (!frame() || !frame()->loader().client())
     return;
 
   ASSERT(isMainThread());
   Document* activeDocument = toDocument(context);
   if (!activeDocument)
     return;
 
   if (!activeDocument->frame() ||
-      !activeDocument->frame()->canNavigate(*frame()))
-    return;
-  if (!NavigationDisablerForUnload::isNavigationAllowed())
+      !activeDocument->frame()->canNavigate(*frame()) ||
+      !activeDocument->frame()->isNavigationAllowed())

[lfg, 2016/11/10 00:15:04]

We should probably merge these two functions, but let's do it in a separate
change.

     return;
 
   // We intentionally call reload() for the current frame if delta is zero.
   // Otherwise, navigation happens on the root frame.
   // This behavior is designed in the following spec.
   // https://html.spec.whatwg.org/multipage/browsers.html#dom-history-go
   if (delta)
     frame()->loader().client()->navigateBackForward(delta);
   else
     frame()->reload(FrameLoadTypeReload, ClientRedirectPolicy::ClientRedirect);
@@ skipping 58 matching lines @@
         frame()->document()->url().elidedString() + "'.");
     return;
   }
 
   frame()->loader().updateForSameDocumentNavigation(
       fullURL, SameDocumentNavigationHistoryApi, std::move(data),
       restorationType, type, frame()->document());
 }
 
 }  // namespace blink