[api] Support sharing prototypes between FunctionTemplates

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 1156 matching lines @@
                               i_isolate);
   if (result->IsUndefined(i_isolate)) {
     // Do not cache prototype objects.
     result = Utils::OpenHandle(
         *ObjectTemplateNew(i_isolate, Local<FunctionTemplate>(), true));
     Utils::OpenHandle(this)->set_prototype_template(*result);
   }
   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) {
   Utils::ApiCheck(!info->instantiated(), func,
                   "FunctionTemplate already instantiated");
 }
 
 
 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));
 }
 
 static Local<FunctionTemplate> FunctionTemplateNew(
     i::Isolate* isolate, FunctionCallback callback,
     experimental::FastAccessorBuilder* fast_handler, v8::Local<Value> data,
     v8::Local<Signature> signature, int length, bool do_not_cache,
     v8::Local<Private> cached_property_name = v8::Local<Private>()) {
   i::Handle<i::Struct> struct_obj =
       isolate->factory()->NewStruct(i::FUNCTION_TEMPLATE_INFO_TYPE);
@@ skipping 8654 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8