[api] Support sharing prototypes between FunctionTemplates

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index a9a17b458bb45330d0a903598b181c51decb5c30..dc410c01af6d0620210ade616f85c57f7dcfd8f9 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -1174,6 +1174,16 @@ Local<ObjectTemplate> FunctionTemplate::PrototypeTemplate() {
   return ToApiHandle<ObjectTemplate>(result);
 }
 
+void FunctionTemplate::SetPrototypeProviderTemplate(
+    Local<FunctionTemplate> prototype_provider) {
+  i::Isolate* i_isolate = Utils::OpenHandle(this)->GetIsolate();
+  ENTER_V8(i_isolate);
+  i::Handle<i::Object> result = Utils::OpenHandle(*prototype_provider);
+  auto info = Utils::OpenHandle(this);
+  CHECK(info->prototype_template()->IsUndefined(i_isolate));
+  CHECK(info->parent_template()->IsUndefined(i_isolate));
+  info->set_prototype_provider_template(*result);
+}
 
 static void EnsureNotInstantiated(i::Handle<i::FunctionTemplateInfo> info,
                                   const char* func) {
@@ -1185,8 +1195,9 @@ static void EnsureNotInstantiated(i::Handle<i::FunctionTemplateInfo> info,
 void FunctionTemplate::Inherit(v8::Local<FunctionTemplate> value) {
   auto info = Utils::OpenHandle(this);
   EnsureNotInstantiated(info, "v8::FunctionTemplate::Inherit");
-  i::Isolate* isolate = info->GetIsolate();
-  ENTER_V8(isolate);
+  i::Isolate* i_isolate = info->GetIsolate();
+  ENTER_V8(i_isolate);
+  CHECK(info->prototype_provider_template()->IsUndefined(i_isolate));
   info->set_parent_template(*Utils::OpenHandle(*value));
 }