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

Source/core/rendering/RenderScrollbar.cpp

Index: Source/core/rendering/RenderScrollbar.cpp
diff --git a/Source/core/rendering/RenderScrollbar.cpp b/Source/core/rendering/RenderScrollbar.cpp
index 9612040262a8f80fdf29d7e69dfc5df7e1506b9d..2cef428a51872a898a697a8833cc90c3da027b5b 100644
--- a/Source/core/rendering/RenderScrollbar.cpp
+++ b/Source/core/rendering/RenderScrollbar.cpp
@@ -252,7 +252,7 @@ void RenderScrollbar::updateScrollbarPart(ScrollbarPart partType, bool destroy)
 
     RenderScrollbarPart* partRenderer = m_parts.get(partType);
     if (!partRenderer && needRenderer) {
-        partRenderer = RenderScrollbarPart::createAnonymous(owningRenderer()->document(), this, partType);
+        partRenderer = RenderScrollbarPart::createAnonymous(&owningRenderer()->document(), this, partType);
         m_parts.set(partType, partRenderer);
     } else if (partRenderer && !needRenderer) {
         m_parts.remove(partType);