Sequential focus navigation across frames should clear per-document starting point.

third_party/WebKit/Source/core/page/FocusController.cpp

 /*
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nuanti Ltd.
  *
  * 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 976 matching lines @@
     DCHECK(element->isFocusable());
 
     // FIXME: It would be nice to just be able to call setFocusedElement(element)
     // here, but we can't do that because some elements (e.g. HTMLInputElement
     // and HTMLTextAreaElement) do extra work in their focus() methods.
     Document& newDocument = element->document();
 
     if (&newDocument != document) {
         // Focus is going away from this document, so clear the focused element.
         document->clearFocusedElement();
+        document->setSequentialFocusNavigationStartingPoint(nullptr);
     }
 
     setFocusedFrame(newDocument.frame());
 
     if (caretBrowsing) {
         Position position = firstPositionInOrBeforeNode(element);
         VisibleSelection newSelection(position, position);
         frame->selection().setSelection(newSelection);
     }
 
@@ skipping 306 matching lines @@
     return consumed;
 }
 
 DEFINE_TRACE(FocusController)
 {
     visitor->trace(m_page);
     visitor->trace(m_focusedFrame);
 }
 
 } // namespace blink