bindings: Use V8 MaybeLocal<> APIs in Dictionary class

Source/bindings/core/v8/Dictionary.h

Index: Source/bindings/core/v8/Dictionary.h
diff --git a/Source/bindings/core/v8/Dictionary.h b/Source/bindings/core/v8/Dictionary.h
index 5860f34414e00be8276216d35edc9ca8d684d6e0..e782ea8512c6fb1f0a4b6e67e6e13b3bb0509552 100644
--- a/Source/bindings/core/v8/Dictionary.h
+++ b/Source/bindings/core/v8/Dictionary.h
@@ -44,7 +44,7 @@ namespace blink {
 // Dictionary class provides ways to retrieve property values as C++ objects
 // from a V8 object. Instances of this class must not outlive V8's handle scope
 // because they hold a V8 value without putting it on persistent handles.
-class Dictionary {
+class Dictionary final {
     ALLOW_ONLY_INLINE_ALLOCATION();
 public:
     Dictionary();
@@ -120,6 +120,9 @@ public:
     bool hasProperty(const String&) const;
 
     v8::Isolate* isolate() const { return m_isolate; }
+    // Used by DictionaryHelper. This context could be an empty handle and
+    // should be used only for V8 APIs which return MaybeLocal<T>.
+    v8::Local<v8::Context> context() const;
 
     bool getKey(const String& key, v8::Local<v8::Value>&) const;