SVGTests should not leave detached elements in the tree

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

 // [Name] SVGForeignObjectElement-svgdom-requiredFeatures.js
 // [Expected rendering result] a series of PASS messages
 
 createSVGTestCase();
 
 var foreignObjectElement = createSVGElement("foreignObject");
 foreignObjectElement.setAttribute("width", "200");
 foreignObjectElement.setAttribute("height", "200");
 
 var htmlDivElement = document.createElementNS(xhtmlNS, "xhtml:div");
 htmlDivElement.setAttribute("style", "background-color: green; color: white; text-align: center");
 htmlDivElement.textContent = "Test passed";
 
 foreignObjectElement.appendChild(htmlDivElement);
 rootSVGElement.appendChild(foreignObjectElement);
 
 function repaintTest() {
     debug("Check that SVGForeignObjectElement is initially displayed");
-    shouldBeEqualToString("document.defaultView.getComputedStyle(foreignObjectElement, null).display", "block");
+    shouldHaveBBox("foreignObjectElement", "200", "200");
     debug("Check that setting requiredFeatures to something invalid makes it not render");
     foreignObjectElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#BogusFeature");
-    shouldBeEqualToString("document.defaultView.getComputedStyle(foreignObjectElement, null).display", "");
+    shouldHaveBBox("foreignObjectElement", "0", "0");
     debug("Check that setting requiredFeatures to something valid makes it render again");
     foreignObjectElement.requiredFeatures.replaceItem("http://www.w3.org/TR/SVG11/feature#Shape", 0);
-    shouldBeEqualToString("document.defaultView.getComputedStyle(foreignObjectElement, null).display", "block");
+    shouldHaveBBox("foreignObjectElement", "200", "200");
     debug("Check that adding something valid to requiredFeatures keeps rendering the element");
     foreignObjectElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#Gradient");
-    shouldBeEqualToString("document.defaultView.getComputedStyle(foreignObjectElement, null).display", "block");
+    shouldHaveBBox("foreignObjectElement", "200", "200");
     debug("Check that adding something invalid to requiredFeatures makes it not render");
     foreignObjectElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#BogusFeature");
-    shouldBeEqualToString("document.defaultView.getComputedStyle(foreignObjectElement, null).display", "");
+    shouldHaveBBox("foreignObjectElement", "0", "0");
 
     completeTest();
 }
 
 var successfullyParsed = true;