Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/svg/SVGFEDiffuseLightingElement.cpp

Index: Source/core/svg/SVGFEDiffuseLightingElement.cpp
diff --git a/Source/core/svg/SVGFEDiffuseLightingElement.cpp b/Source/core/svg/SVGFEDiffuseLightingElement.cpp
index 328ad94d002d4634a80cda1676517d82ea6abc33..09cb7f2910d3df4d05fcfda75dc68d3e60a93cff 100644
--- a/Source/core/svg/SVGFEDiffuseLightingElement.cpp
+++ b/Source/core/svg/SVGFEDiffuseLightingElement.cpp
@@ -177,15 +177,15 @@ PassRefPtr<FilterEffect> SVGFEDiffuseLightingElement::build(SVGFilterBuilder* fi
     FilterEffect* input1 = filterBuilder->getEffectById(AtomicString(m_in1->currentValue()->value()));
 
     if (!input1)
-        return 0;
+        return nullptr;
 
     RefPtr<LightSource> lightSource = SVGFELightElement::findLightSource(this);
     if (!lightSource)
-        return 0;
+        return nullptr;
 
     RenderObject* renderer = this->renderer();
     if (!renderer)
-        return 0;
+        return nullptr;
 
     ASSERT(renderer->style());
     Color color = renderer->style()->svgStyle()->lightingColor();