[WIP] bindings: Introduce PropertyBag

Source/bindings/templates/interface.h

Index: Source/bindings/templates/interface.h
diff --git a/Source/bindings/templates/interface.h b/Source/bindings/templates/interface.h
index 4c09d08af9ebd0827d0a0e588fac81e867ba951d..f0acb56c62b0a6cda9468ba466487b472bec319e 100644
--- a/Source/bindings/templates/interface.h
+++ b/Source/bindings/templates/interface.h
@@ -15,7 +15,7 @@
 namespace blink {
 
 {% if has_event_constructor %}
-class Dictionary;
+class PropertyBag;
 {% endif %}
 {% if named_constructor %}
 class {{v8_class}}Constructor {
@@ -286,9 +286,14 @@ inline void v8SetReturnValueFast(const CallbackInfo& callbackInfo, {{pass_cpp_ty
 }
 
 {% if has_event_constructor %}
-bool initialize{{cpp_class}}({{cpp_class}}Init&, const Dictionary&, ExceptionState&, const v8::FunctionCallbackInfo<v8::Value>& info, const String& = "");
+bool initialize{{cpp_class}}({{cpp_class}}Init&, const PropertyBag&, ExceptionState&, const v8::FunctionCallbackInfo<v8::Value>& info, const String& = "");
 
 {% endif %}
+template <>
+struct PropertyBagTraits<{{cpp_class}}> {
+    typedef {{v8_class}} type;
+};
+
 } // namespace blink
 {% endfilter %}
 #endif // {{v8_class}}_h