WIP [esnext] implement async iteration proposal

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index ee39fdd069c43bd2b35e2ccf27ac6ef21a3a3aed..93f9f03c12c634419f81059247b254f63e5a950d 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -109,6 +109,8 @@ void HeapObject::HeapObjectVerify() {
     case JS_GENERATOR_OBJECT_TYPE:
       JSGeneratorObject::cast(this)->JSGeneratorObjectVerify();
       break;
+    case JS_ASYNC_GENERATOR_OBJECT_TYPE:
+      JSAsyncGeneratorObject::cast(this)->JSAsyncGeneratorObjectVerify();
     case JS_VALUE_TYPE:
       JSValue::cast(this)->JSValueVerify();
       break;
@@ -477,6 +479,12 @@ void JSGeneratorObject::JSGeneratorObjectVerify() {
   VerifyObjectField(kContinuationOffset);
 }
 
+void JSAsyncGeneratorObject::JSAsyncGeneratorObjectVerify() {
+  // Check inherited fields
+  JSGeneratorObjectVerify();
+  VerifyObjectField(kQueueOffset);
+  queue()->HeapObjectVerify();
+}
 
 void JSValue::JSValueVerify() {
   Object* v = value();
@@ -1057,6 +1065,17 @@ void PromiseReactionJobInfo::PromiseReactionJobInfoVerify() {
   CHECK(context()->IsContext());
 }
 
+void AsyncGeneratorRequest::AsyncGeneratorRequestVerify() {
+  CHECK(IsAsyncGeneratorRequest());
+  VerifySmiField(kResumeModeOffset);
+  CHECK_GE(resume_mode(), JSGeneratorObject::kNext);
+  CHECK_LE(resume_mode(), JSGeneratorObject::kThrow);
+  CHECK(promise()->IsJSPromise());
+  VerifyPointer(value());
+  VerifyPointer(next());
+  next()->ObjectVerify();
+}
+
 void JSModuleNamespace::JSModuleNamespaceVerify() {
   CHECK(IsJSModuleNamespace());
   VerifyPointer(module());