IDL: Add PropertyBag class

Source/bindings/templates/dictionary_v8.cpp

Index: Source/bindings/templates/dictionary_v8.cpp
diff --git a/Source/bindings/templates/dictionary_v8.cpp b/Source/bindings/templates/dictionary_v8.cpp
index 76240ac35cc94f2477e15d0090d640b11683ce5b..24e9152490635dd0ce40c9e2dbe22b7404d7a743 100644
--- a/Source/bindings/templates/dictionary_v8.cpp
+++ b/Source/bindings/templates/dictionary_v8.cpp
@@ -16,12 +16,13 @@ namespace blink {
 {{cpp_class}}* {{v8_class}}::toNative(v8::Isolate* isolate, v8::Handle<v8::Value> v8Value)
 {
     {{cpp_class}}* impl = {{cpp_class}}::create();
-    // FIXME: Do not use Dictionary and DictionaryHelper
-    // https://crbug.com/321462
-    Dictionary dictionary(v8Value, isolate);
+    if (v8Value.IsEmpty() || !v8Value->IsObject())
+        return impl;
+    v8::Local<v8::Object> v8Object = v8Value->ToObject();
+    PropertyBag bag(isolate, v8Object);
     {% for member in members %}
     {{member.cpp_type}} {{member.name}};
-    if (DictionaryHelper::get(dictionary, "{{member.name}}", {{member.name}}))
+    if (bag.get("{{member.name}}", {{member.name}}))
         impl->{{member.setter_name}}({{member.name}});
     {% endfor %}
     return impl;