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

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index fc70d14a59351ddd55664b363a1ab122e26b7481..c52e8c4d3d776a373c1a6e92aaa0af0c743af902 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1387,6 +1387,30 @@ void Document::unregisterVisibilityObserver(DocumentVisibilityObserver* 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";