Fix crash when a demoted FORM element is moved into a ShadowRoot.

Source/core/html/HTMLFormElement.cpp

Index: Source/core/html/HTMLFormElement.cpp
diff --git a/Source/core/html/HTMLFormElement.cpp b/Source/core/html/HTMLFormElement.cpp
index 806610fefecc0bc07bca1908c800eaff85e547df..2e03d062be0f554693537bc13d52e3231729a2fb 100644
--- a/Source/core/html/HTMLFormElement.cpp
+++ b/Source/core/html/HTMLFormElement.cpp
@@ -92,6 +92,8 @@ bool HTMLFormElement::rendererIsNeeded(const RenderStyle& style)
         return HTMLElement::rendererIsNeeded(style);
 
     ContainerNode* node = parentNode();
+    if (!node || !node->renderer())
+        return HTMLElement::rendererIsNeeded(style);
     RenderObject* parentRenderer = node->renderer();
     // FIXME: Shouldn't we also check for table caption (see |formIsTablePart| below).
     // FIXME: This check is not correct for Shadow DOM.