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

Source/core/rendering/RenderLayerFilterInfo.cpp

Index: Source/core/rendering/RenderLayerFilterInfo.cpp
diff --git a/Source/core/rendering/RenderLayerFilterInfo.cpp b/Source/core/rendering/RenderLayerFilterInfo.cpp
index 89af94203859218cbd27039b42656fe24e4ba632..b89d660c6107c9dc6dec57252585efaba715a217 100644
--- a/Source/core/rendering/RenderLayerFilterInfo.cpp
+++ b/Source/core/rendering/RenderLayerFilterInfo.cpp
@@ -126,7 +126,7 @@ void RenderLayerFilterInfo::updateReferenceFilterClients(const FilterOperations&
         } else {
             // Reference is internal; add layer as a client so we can trigger
             // filter repaint on SVG attribute change.
-            Element* filter = m_layer->renderer()->node()->document()->getElementById(referenceFilterOperation->fragment());
+            Element* filter = m_layer->renderer()->node()->document().getElementById(referenceFilterOperation->fragment());
             if (!filter || !filter->hasTagName(SVGNames::filterTag))
                 continue;
             toSVGFilterElement(filter)->addClientRenderLayer(m_layer);