Fix the places where we forward declare mozilla::dom::Nullable as a class, no bug, r=I'm-sick-and-tired-of-MSVC-stupidity

content/html/content/src/HTMLFormControlsCollection.h

@@ -21,7 +21,7 @@ namespace dom {
 class HTMLFormElement;
 class HTMLImageElement;
 class OwningNodeListOrElement;
-template<typename> class Nullable;
+template<typename> struct Nullable;
 
 class HTMLFormControlsCollection : public nsIHTMLCollection
                                  , public nsWrapperCache

content/html/document/src/HTMLAllCollection.h

@@ -27,7 +27,7 @@ class ErrorResult;
 namespace dom {
 
 class OwningNodeOrHTMLCollection;
-template<typename> class Nullable;
+template<typename> struct Nullable;
 
 class HTMLAllCollection MOZ_FINAL : public nsISupports
                                   , public nsWrapperCache