Bug 1564449, ensure the right body element is used throughout the method call, r=mccr8

dom/html/ImageDocument.cpp

@@ -657,7 +657,7 @@ nsresult ImageDocument::CreateSyntheticDocument() {
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Add the image element
-  Element* body = GetBodyElement();
+  RefPtr<Element> body = GetBodyElement();
   if (!body) {
     NS_WARNING("no body on image document!");
     return NS_ERROR_FAILURE;

dom/html/PluginDocument.cpp

@@ -190,7 +190,7 @@ nsresult PluginDocument::CreateSyntheticPluginDocument() {
   NS_ENSURE_SUCCESS(rv, rv);
   // then attach our plugin
 
-  Element* body = GetBodyElement();
+  RefPtr<Element> body = GetBodyElement();
   if (!body) {
     NS_WARNING("no body on plugin document!");
     return NS_ERROR_FAILURE;

dom/html/VideoDocument.cpp

@@ -102,7 +102,7 @@ void VideoDocument::SetScriptGlobalObject(
 }
 
 nsresult VideoDocument::CreateVideoElement() {
-  Element* body = GetBodyElement();
+  RefPtr<Element> body = GetBodyElement();
   if (!body) {
     NS_WARNING("no body on video document!");
     return NS_ERROR_FAILURE;