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

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 97 matching lines @@
 #include "core/layout/LayoutTextFragment.h"
 #include "core/layout/LayoutView.h"
 #include "core/loader/DocumentLoader.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/FocusController.h"
 #include "core/page/Page.h"
 #include "core/page/PointerLockController.h"
 #include "core/page/SpatialNavigation.h"
 #include "core/page/scrolling/ScrollState.h"
 #include "core/paint/DeprecatedPaintLayer.h"
+#include "core/style/StyleObserver.h"
 #include "core/svg/SVGDocumentExtensions.h"
 #include "core/svg/SVGElement.h"
 #include "platform/EventDispatchForbiddenScope.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/UserGestureIndicator.h"
 #include "platform/scroll/ScrollableArea.h"
 #include "wtf/BitVector.h"
 #include "wtf/HashFunctions.h"
 #include "wtf/text/CString.h"
 #include "wtf/text/StringBuilder.h"
@@ skipping 1574 matching lines @@
         reattachContext.resolvedStyle = newStyle.get();
         bool layoutObjectWillChange = needsAttach() || layoutObject();
         reattach(reattachContext);
         if (layoutObjectWillChange || layoutObject())
             return Reattach;
         return ReattachNoLayoutObject;
     }
 
     ASSERT(oldStyle);
 
-    if (localChange != NoChange)
+    if (localChange != NoChange) {
+        if (document().hasStyleObserver())
+            document().notifyStyleObservers(this, oldStyle.get(), newStyle.get());
         updateCallbackSelectors(oldStyle.get(), newStyle.get());
+    }
 
     if (LayoutObject* layoutObject = this->layoutObject()) {
         if (localChange != NoChange || pseudoStyleCacheIsInvalid(oldStyle.get(), newStyle.get()) || svgFilterNeedsLayerUpdate()) {
             layoutObject->setStyle(newStyle.get());
         } else {
             // Although no change occurred, we use the new style so that the cousin style sharing code won't get
             // fooled into believing this style is the same.
             // FIXME: We may be able to remove this hack, see discussion in
             // https://codereview.chromium.org/30453002/
             layoutObject->setStyleInternal(newStyle.get());
@@ skipping 1777 matching lines @@
 {
 #if ENABLE(OILPAN)
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
 #endif
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink