Have Document::accessSVGExtensions() return a reference

Source/core/rendering/svg/SVGResourcesCache.cpp

Index: Source/core/rendering/svg/SVGResourcesCache.cpp
diff --git a/Source/core/rendering/svg/SVGResourcesCache.cpp b/Source/core/rendering/svg/SVGResourcesCache.cpp
index f0a3365b9de6c6ef69ad5405442512fe9ef1e38c..c5cc3dc4b416ebac8695ee6368cd1e012149e25b 100644
--- a/Source/core/rendering/svg/SVGResourcesCache.cpp
+++ b/Source/core/rendering/svg/SVGResourcesCache.cpp
@@ -85,10 +85,8 @@ static inline SVGResourcesCache* resourcesCacheFromRenderObject(const RenderObje
 {
     Document& document = renderer->document();
 
-    SVGDocumentExtensions* extensions = document.accessSVGExtensions();
-    ASSERT(extensions);
-
-    SVGResourcesCache* cache = extensions->resourcesCache();
+    SVGDocumentExtensions& extensions = document.accessSVGExtensions();
+    SVGResourcesCache* cache = extensions.resourcesCache();
     ASSERT(cache);
 
     return cache;
@@ -194,9 +192,9 @@ void SVGResourcesCache::resourceDestroyed(RenderSVGResourceContainer* resource)
         // Mark users of destroyed resources as pending resolution based on the id of the old resource.
         Element* resourceElement = resource->element();
         Element* clientElement = toElement(it->key->node());
-        SVGDocumentExtensions* extensions = clientElement->document().accessSVGExtensions();
+        SVGDocumentExtensions& extensions = clientElement->document().accessSVGExtensions();
 
-        extensions->addPendingResource(resourceElement->fastGetAttribute(HTMLNames::idAttr), clientElement);
+        extensions.addPendingResource(resourceElement->fastGetAttribute(HTMLNames::idAttr), clientElement);
     }
 }