Have Document::accessSVGExtensions() return a reference

Have Document::accessSVGExtensions() return a reference
https://bugs.webkit.org/show_bug.cgi?id=137030

Reviewed by Ryosuke Niwa.

Have Document::accessSVGExtensions() return a reference instead of a
pointer as it can never return null.

No new tests, no behavior change.

* dom/ContainerNode.cpp:
(WebCore::ContainerNode::removeChild):
(WebCore::ContainerNode::removeChildren):
* dom/Document.cpp:
(WebCore::Document::commonTeardown):
(WebCore::Document::implicitClose):
(WebCore::Document::accessSVGExtensions):
* dom/Document.h:
* dom/Element.cpp:
(WebCore::Element::~Element):
(WebCore::Element::removedFrom):
* editing/markup.cpp:
(WebCore::isPlainTextMarkup):
* history/CachedFrame.cpp:
(WebCore::CachedFrameBase::restore):
* rendering/FilterEffectRenderer.cpp:
(WebCore::FilterEffectRenderer::buildReferenceFilter):
* rendering/svg/RenderSVGResource.cpp:
(WebCore::removeFromCacheAndInvalidateDependencies):
* rendering/svg/RenderSVGResourceContainer.cpp:
(WebCore::svgExtensionsFromElement):
* rendering/svg/RenderSVGResourceContainer.h:
(WebCore::getRenderSVGResourceContainerById):
(WebCore::getRenderSVGResourceById):
* rendering/svg/SVGResources.cpp:
(WebCore::registerPendingResource):
(WebCore::SVGResources::buildCachedResources):
* rendering/svg/SVGResourcesCache.cpp:
(WebCore::resourcesCacheFromRenderer):
(WebCore::SVGResourcesCache::resourceDestroyed):
* svg/SVGElement.cpp:
(WebCore::SVGElement::~SVGElement):
(WebCore::SVGElement::reportAttributeParsingError):
(WebCore::SVGElement::removedFrom):
(WebCore::SVGElement::viewportElement):
(WebCore::SVGElement::attributeChanged):
(WebCore::SVGElement::buildPendingResourcesIfNeeded):
(WebCore::SVGElement::accessDocumentSVGExtensions): Deleted.
* svg/SVGElement.h:
* svg/SVGFEConvolveMatrixElement.cpp:
(WebCore::SVGFEConvolveMatrixElement::parseAttribute):
* svg/SVGFEGaussianBlurElement.cpp:
(WebCore::SVGFEGaussianBlurElement::parseAttribute):
* svg/SVGFEImageElement.cpp:
(WebCore::SVGFEImageElement::clearResourceReferences):
(WebCore::SVGFEImageElement::buildPendingResource):
* svg/SVGFitToViewBox.cpp:
(WebCore::SVGFitToViewBox::parseViewBox):
* svg/SVGFontFaceElement.cpp:
(WebCore::SVGFontFaceElement::insertedInto):
(WebCore::SVGFontFaceElement::removedFrom):
* svg/SVGMPathElement.cpp:
(WebCore::SVGMPathElement::buildPendingResource):
(WebCore::SVGMPathElement::clearResourceReferences):
* svg/SVGPathElement.cpp:
(WebCore::SVGPathElement::parseAttribute):
(WebCore::SVGPathElement::invalidateMPathDependencies):
* svg/SVGPolyElement.cpp:
(WebCore::SVGPolyElement::parseAttribute):
* svg/SVGSVGElement.cpp:
(WebCore::SVGSVGElement::~SVGSVGElement):
(WebCore::SVGSVGElement::insertedInto):
(WebCore::SVGSVGElement::removedFrom):
* svg/SVGTRefElement.cpp:
(WebCore::SVGTRefElement::detachTarget):
(WebCore::SVGTRefElement::buildPendingResource):
* svg/SVGTextPathElement.cpp:
(WebCore::SVGTextPathElement::clearResourceReferences):
(WebCore::SVGTextPathElement::buildPendingResource):
* svg/SVGUseElement.cpp:
(WebCore::SVGUseElement::clearResourceReferences):
(WebCore::SVGUseElement::buildPendingResource):
(WebCore::SVGUseElement::toClipPath):
(WebCore::SVGUseElement::buildInstanceTree):
* svg/animation/SVGSMILElement.cpp:
(WebCore::SVGSMILElement::clearResourceReferences):
(WebCore::SVGSMILElement::buildPendingResource):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@173883 268f45cc-cd09-0410-ab3c-d52691b4dbfc