Bug 1272442. Make RootedDictionary, NullableRootedDictionary and SequenceRooter final. r=ehsan

This eliminates a bunch of clang warnings.

dom/bindings/BindingUtils.h

@@ -2273,7 +2273,7 @@ void DoTraceSequence(JSTracer* trc, InfallibleTArray<T>& seq)
 
 // Rooter class for sequences; this is what we mostly use in the codegen
 template<typename T>
-class MOZ_RAII SequenceRooter : private JS::CustomAutoRooter
+class MOZ_RAII SequenceRooter final : private JS::CustomAutoRooter
 {
 public:
   SequenceRooter(JSContext *aCx, FallibleTArray<T>* aSequence

dom/bindings/RootedDictionary.h

@@ -15,7 +15,7 @@ namespace mozilla {
 namespace dom {
 
 template<typename T>
-class MOZ_RAII RootedDictionary : public T,
+class MOZ_RAII RootedDictionary final : public T,
                                          private JS::CustomAutoRooter
 {
 public:
@@ -32,7 +32,7 @@ public:
 };
 
 template<typename T>
-class MOZ_RAII NullableRootedDictionary : public Nullable<T>,
+class MOZ_RAII NullableRootedDictionary final : public Nullable<T>,
                                                  private JS::CustomAutoRooter
 {
 public: