Re-land FastAccessorBuilder.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 9544a0e32ccda78f9e5d949890ec07bcd121c29a..4cd54de0b848d59d9d2724729e46ecfd77a1506d 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -12,8 +12,10 @@
 #include <limits>
 #include <vector>
 #include "include/v8-debug.h"
+#include "include/v8-experimental.h"
 #include "include/v8-profiler.h"
 #include "include/v8-testing.h"
+#include "src/api-experimental.h"
 #include "src/api-natives.h"
 #include "src/assert-scope.h"
 #include "src/background-parsing-task.h"
@@ -999,7 +1001,7 @@ void FunctionTemplate::Inherit(v8::Local<FunctionTemplate> value) {
 
 static Local<FunctionTemplate> FunctionTemplateNew(
     i::Isolate* isolate, FunctionCallback callback,
-    v8::Local<Value> fast_handler, v8::Local<Value> data,
+    experimental::FastAccessorBuilder* fast_handler, v8::Local<Value> data,
     v8::Local<Signature> signature, int length, bool do_not_cache) {
   i::Handle<i::Struct> struct_obj =
       isolate->factory()->NewStruct(i::FUNCTION_TEMPLATE_INFO_TYPE);
@@ -1040,14 +1042,15 @@ Local<FunctionTemplate> FunctionTemplate::New(Isolate* isolate,
   DCHECK(!i_isolate->serializer_enabled());
   LOG_API(i_isolate, "FunctionTemplate::New");
   ENTER_V8(i_isolate);
-  return FunctionTemplateNew(i_isolate, callback, v8::Local<Value>(), data,
-                             signature, length, false);
+  return FunctionTemplateNew(i_isolate, callback, nullptr, data, signature,
+                             length, false);
 }
 
 
 Local<FunctionTemplate> FunctionTemplate::NewWithFastHandler(
-    Isolate* isolate, FunctionCallback callback, v8::Local<Value> fast_handler,
-    v8::Local<Value> data, v8::Local<Signature> signature, int length) {
+    Isolate* isolate, FunctionCallback callback,
+    experimental::FastAccessorBuilder* fast_handler, v8::Local<Value> data,
+    v8::Local<Signature> signature, int length) {
   // TODO(vogelheim): 'fast_handler' should have a more specific type than
   // Local<Value>.
   i::Isolate* i_isolate = reinterpret_cast<i::Isolate*>(isolate);
@@ -1077,9 +1080,9 @@ Local<AccessorSignature> AccessorSignature::New(
   } while (false)
 
 
-void FunctionTemplate::SetCallHandler(FunctionCallback callback,
-                                      v8::Local<Value> data,
-                                      v8::Local<Value> fast_handler) {
+void FunctionTemplate::SetCallHandler(
+    FunctionCallback callback, v8::Local<Value> data,
+    experimental::FastAccessorBuilder* fast_handler) {
   auto info = Utils::OpenHandle(this);
   EnsureNotInstantiated(info, "v8::FunctionTemplate::SetCallHandler");
   i::Isolate* isolate = info->GetIsolate();
@@ -1090,10 +1093,10 @@ void FunctionTemplate::SetCallHandler(FunctionCallback callback,
   i::Handle<i::CallHandlerInfo> obj =
       i::Handle<i::CallHandlerInfo>::cast(struct_obj);
   SET_FIELD_WRAPPED(obj, set_callback, callback);
-  if (!fast_handler.IsEmpty()) {
-    i::Handle<i::Object> code = Utils::OpenHandle(*fast_handler);
-    CHECK(code->IsCode());
-    obj->set_fast_handler(*code);
+  i::MaybeHandle<i::Code> code =
+      i::experimental::BuildCodeFromFastAccessorBuilder(fast_handler);
+  if (!code.is_null()) {
+    obj->set_fast_handler(*code.ToHandleChecked());
   }
   if (data.IsEmpty()) {
     data = v8::Undefined(reinterpret_cast<v8::Isolate*>(isolate));
@@ -4368,7 +4371,7 @@ MaybeLocal<Function> Function::New(Local<Context> context,
   i::Isolate* isolate = Utils::OpenHandle(*context)->GetIsolate();
   LOG_API(isolate, "Function::New");
   ENTER_V8(isolate);
-  return FunctionTemplateNew(isolate, callback, Local<Value>(), data,
+  return FunctionTemplateNew(isolate, callback, nullptr, data,
                              Local<Signature>(), length, true)
       ->GetFunction(context);
 }