Add the c++ code part of bindings2/

sky/engine/bindings2/scripts/templates/attributes_cpp.template

Index: sky/engine/bindings2/scripts/templates/attributes_cpp.template
diff --git a/sky/engine/bindings2/scripts/templates/attributes_cpp.template b/sky/engine/bindings2/scripts/templates/attributes_cpp.template
index 5d6c7aa347b45c9f84b2411ce678138268641265..cc0184087c4041bb18f2d9a43c204833c1e93895 100644
--- a/sky/engine/bindings2/scripts/templates/attributes_cpp.template
+++ b/sky/engine/bindings2/scripts/templates/attributes_cpp.template
@@ -8,7 +8,7 @@ static void {{static_attribute_name(attribute, 'Getter')}}(Dart_NativeArguments
 {% if attribute.is_call_with_execution_context %}
     ExecutionContext* context = DOMDartState::CurrentDocument();
     if (!context) {
-      exception = Dart_NewStringFromCString("Failed to retrieve a context");
+      exception = ToDart("Failed to retrieve a context");
       goto fail;
     }
 {% endif %}
@@ -95,7 +95,7 @@ static void {{static_attribute_name(attribute, 'Setter')}}(Dart_NativeArguments
 
         ExecutionContext* context = DOMDartState::CurrentDocument();
         if (!context) {
-            exception = Dart_NewStringFromCString("Failed to retrieve a context");
+            exception = ToDart("Failed to retrieve a context");
             goto fail;
         }
 
@@ -104,7 +104,7 @@ static void {{static_attribute_name(attribute, 'Setter')}}(Dart_NativeArguments
 {% if attribute.is_call_with_script_state %}
         ScriptState* state = DartUtilities::currentScriptState();
         if (!state) {
-            exception = Dart_NewStringFromCString("Failed to retrieve a script state");
+            exception = ToDart("Failed to retrieve a script state");
             goto fail;
         }
 {% endif %}