WIP - Rough draft of style observation in style of apply hooks.

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.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 1369 matching lines @@
     ASSERT(!m_visibilityObservers.contains(observer));
     m_visibilityObservers.add(observer);
 }
 
 void Document::unregisterVisibilityObserver(DocumentVisibilityObserver* observer)
 {
     ASSERT(m_visibilityObservers.contains(observer));
     m_visibilityObservers.remove(observer);
 }
 
+bool Document::hasStyleObserver()
+{
+    return !m_styleObservers.isEmpty();
+}
+
+void Document::notifyStyleObservers(const Element* element, const ComputedStyle* oldStyle, const ComputedStyle* newStyle)
+{
+    // TODO(majidvp): make a snapshot of observers to avoid them being changed while we iterate
+    for (StyleObserver* observer : m_styleObservers)
+        observer->onStyleChanged(element, oldStyle, newStyle);
+}
+
+void Document::registerStyleObserver(StyleObserver* observer)
+{
+    ASSERT(!m_styleObservers.contains(observer));
+    m_styleObservers.add(observer);
+}
+
+void Document::unregisterStyleObserver(StyleObserver* observer)
+{
+    ASSERT(m_styleObservers.contains(observer));
+    m_styleObservers.remove(observer);
+}
+
 String Document::nodeName() const
 {
     return "#document";
 }
 
 Node::NodeType Document::nodeType() const
 {
     return DOCUMENT_NODE;
 }
 
@@ skipping 4293 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     Document::WeakDocumentSet& set = Document::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().string().utf8().data());
 }
 #endif