binding: Changes the association among global-proxy/global/window-instance.

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 5190 matching lines @@
 
 HTMLCollection* Document::windowNamedItems(const AtomicString& name) {
   return ensureCachedCollection<WindowNameCollection>(WindowNamedItems, name);
 }
 
 DocumentNameCollection* Document::documentNamedItems(const AtomicString& name) {
   return ensureCachedCollection<DocumentNameCollection>(DocumentNamedItems,
                                                         name);
 }
 
+LocalDOMWindow* Document::defaultView() const {
+  return m_frame ? m_domWindow : nullptr;

[haraken, 2017/02/09 12:46:40]

Would you help me understand why we need to check m_frame?

[Yuki, 2017/02/10 07:47:21]

https://html.spec.whatwg.org/multipage/browsers.html#dom-document-defaultview
The defaultView IDL attribute of the Document interface, on getting, must return
this Document's browsing context's WindowProxy object, if this Document has an
associated browsing context, or null otherwise.

The last phrase "or null otherwise" is important here.  We need to return
nullptr if no |m_frame|.  FYI, we have a layout test, that fails if we ignore
m_frame.

[haraken, 2017/02/10 07:59:40]

I'm wondering why this cannot be 'return m_domWindow'.

It looks like that there's a subtle difference between when m_domWindow is
cleared and when m_frame is cleared, but does it matter here?

[Yuki, 2017/02/10 08:18:19]

I read code a little, and found that
- m_domWindow is cleared by Document::clearDOMWindow
- clearDOMWindow is called only through
  LocalDOMWindow::installNewDocument
  => LocalDOMWindow::clearDocument
     => Document::clearDOMWindow
This doesn't help much to determine if the document is detached from a frame or
not.  Unless the new document is installed, m_domWindow never gets cleared.

[haraken, 2017/02/10 09:15:31]

Makes sense. Can you add a comment about it?

[Yuki, 2017/02/10 11:22:47]

Done.

+}
+
 void Document::finishedParsing() {
   DCHECK(!scriptableDocumentParser() || !m_parser->isParsing());
   DCHECK(!scriptableDocumentParser() || m_readyState != Loading);
   setParsingState(InDOMContentLoaded);
   DocumentParserTiming::from(*this).markParserStop();
 
   // FIXME: DOMContentLoaded is dispatched synchronously, but this should be
   // dispatched in a queued task, see https://crbug.com/425790
   if (!m_documentTiming.domContentLoadedEventStart())
     m_documentTiming.markDomContentLoadedEventStart();
@@ skipping 1350 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->url().getString().utf8().data());
 }
 #endif