Remove DocumentVisibilityObserver

sky/engine/core/dom/Document.h

Index: sky/engine/core/dom/Document.h
diff --git a/sky/engine/core/dom/Document.h b/sky/engine/core/dom/Document.h
index 83322c56da9f1f4fb3bd81ad3cb91b903f5e4878..d8dbea8174a9c4e57420f0424d779b0cf8fc0e5c 100644
--- a/sky/engine/core/dom/Document.h
+++ b/sky/engine/core/dom/Document.h
@@ -146,25 +146,6 @@ typedef unsigned char DocumentClassFlags;
 
 class Document;
 
-class DocumentVisibilityObserver {
-public:
-    DocumentVisibilityObserver(Document&);
-    virtual ~DocumentVisibilityObserver();
-
-    virtual void didChangeVisibilityState(PageVisibilityState) = 0;
-
-    // Classes that inherit Node and DocumentVisibilityObserver must have a
-    // virtual override of Node::didMoveToNewDocument that calls
-    // DocumentVisibilityObserver::setDocument
-    void setObservedDocument(Document&);
-
-private:
-    void registerObserver(Document&);
-    void unregisterObserver();
-
-    RawPtr<Document> m_document;
-};
-
 class Document : public ContainerNode, public TreeScope, public ExecutionContext, public ExecutionContextClient
     , public DocumentSupplementable, public LifecycleContext<Document>, public ResourceClient {
     DEFINE_WRAPPERTYPEINFO();
@@ -617,9 +598,6 @@ public:
     bool hasViewportUnits() const { return m_hasViewportUnits; }
     void notifyResizeForViewportUnits();
 
-    void registerVisibilityObserver(DocumentVisibilityObserver*);
-    void unregisterVisibilityObserver(DocumentVisibilityObserver*);
-
     void didRecalculateStyleForElement() { ++m_styleRecalcElementCounter; }
 
     virtual v8::Handle<v8::Object> wrap(v8::Handle<v8::Object> creationContext, v8::Isolate*) override;
@@ -831,9 +809,6 @@ private:
 
     bool m_hasViewportUnits;
 
-    typedef HashSet<RawPtr<DocumentVisibilityObserver> > DocumentVisibilityObserverSet;
-    DocumentVisibilityObserverSet m_visibilityObservers;
-
     int m_styleRecalcElementCounter;
     mutable DocumentLoadTiming m_documentLoadTiming;
 };