Make DOMImplementation.hasFeature() always return true.

LayoutTests/svg/dynamic-updates/script-tests/SVGUseElement-svgdom-requiredFeatures.js

-// [Name] SVGUseElement-svgdom-requiredFeatures.js
-// [Expected rendering result] a series of PASS messages
-
-createSVGTestCase();
-
-var useElement = createSVGElement("use");
-var defsElement = createSVGElement("defs");
-var rectElement = createSVGElement("rect");
-rectElement.setAttribute("width", "200");
-rectElement.setAttribute("height", "200");
-rectElement.setAttribute("id", "MyRect");
-useElement.setAttributeNS(xlinkNS, "xlink:href", "#MyRect");
-
-defsElement.appendChild(rectElement);
-rootSVGElement.appendChild(defsElement);
-rootSVGElement.appendChild(useElement);
-
-function repaintTest() {
-    debug("Check that SVGUseElement is initially displayed");
-    shouldHaveBBox("useElement", "200", "200");
-    debug("Check that setting requiredFeatures to something invalid makes it not render");
-    useElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#BogusFeature");
-    shouldHaveBBox("useElement", "0", "0");
-    debug("Check that setting requiredFeatures to something valid makes it render again");
-    useElement.requiredFeatures.replaceItem("http://www.w3.org/TR/SVG11/feature#Shape", 0);
-    shouldHaveBBox("useElement", "200", "200");
-    debug("Check that adding something valid to requiredFeatures keeps rendering the element");
-    useElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#Gradient");
-    shouldHaveBBox("useElement", "200", "200");
-    debug("Check that adding something invalid to requiredFeatures makes it not render");
-    useElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#BogusFeature");
-    shouldHaveBBox("useElement", "0", "0");
-}
-
-var successfullyParsed = true;