Have Node::document() return a reference instead of a pointer

Source/core/svg/SVGStyleElement.h

Index: Source/core/svg/SVGStyleElement.h
diff --git a/Source/core/svg/SVGStyleElement.h b/Source/core/svg/SVGStyleElement.h
index 17f89d75d38e45f3e2141d13b3e71d8775e50163..dce609738347581626c752370d1420f847c832f6 100644
--- a/Source/core/svg/SVGStyleElement.h
+++ b/Source/core/svg/SVGStyleElement.h
@@ -60,8 +60,8 @@ private:
     virtual bool rendererIsNeeded(const NodeRenderingContext&) OVERRIDE { return false; }
 
     virtual bool isLoading() const { return StyleElement::isLoading(); }
-    virtual bool sheetLoaded() { return StyleElement::sheetLoaded(document()); }
-    virtual void startLoadingDynamicSheet() { StyleElement::startLoadingDynamicSheet(document()); }
+    virtual bool sheetLoaded() { return StyleElement::sheetLoaded(&document()); }
+    virtual void startLoadingDynamicSheet() { StyleElement::startLoadingDynamicSheet(&document()); }
     virtual Timer<SVGElement>* svgLoadEventTimer() OVERRIDE { return &m_svgLoadEventTimer; }
 
     Timer<SVGElement> m_svgLoadEventTimer;