[Extension Bindings] Add JS custom hook support

extensions/renderer/api_bindings_system.h

Index: extensions/renderer/api_bindings_system.h
diff --git a/extensions/renderer/api_bindings_system.h b/extensions/renderer/api_bindings_system.h
index 844051cc6cc528525721ed57b2e54b54e8c0c933..72f77259b98a66ee87c46805a986e81920550349 100644
--- a/extensions/renderer/api_bindings_system.h
+++ b/extensions/renderer/api_bindings_system.h
@@ -105,6 +105,8 @@ class APIBindingsSystem {
   // performance concern?
   std::map<std::string, std::unique_ptr<APIBindingHooks>> binding_hooks_;
 
+  binding::RunJSFunction call_js_;
+
   // The method to retrieve the DictionaryValue describing a given extension
   // API. Curried in for testing purposes so we can use fake APIs.
   GetAPISchemaMethod get_api_schema_;