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

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index c8033444844eb4eadf59ca737ca7a7b009a090f6..549ab306f3b1aec6dbff9af7f029c4cfdf374c35 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -115,6 +115,7 @@
 #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"
@@ -1709,8 +1710,11 @@ StyleRecalcChange Element::recalcOwnStyle(StyleRecalcChange change)
 
     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()) {