[esnext] prototype runtime implementation for async functions

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index ca4f2c4163290be5d1a4f58e4168817c2e37188e..8bd8b2b6c792e26c7488b5219674007755ee7bb9 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -943,7 +943,8 @@ enum FunctionKind {
   kClassConstructor =
       kBaseConstructor | kSubclassConstructor | kDefaultConstructor,
   kAsyncArrowFunction = kArrowFunction | kAsyncFunction,
-  kAsyncConciseMethod = kAsyncFunction | kConciseMethod
+  kAsyncConciseMethod = kAsyncFunction | kConciseMethod,
+  kArrowGeneratorFunction = kGeneratorFunction | kArrowFunction
 };
 
 inline bool IsValidFunctionKind(FunctionKind kind) {
@@ -961,7 +962,8 @@ inline bool IsValidFunctionKind(FunctionKind kind) {
          kind == FunctionKind::kSubclassConstructor ||
          kind == FunctionKind::kAsyncFunction ||
          kind == FunctionKind::kAsyncArrowFunction ||
-         kind == FunctionKind::kAsyncConciseMethod;
+         kind == FunctionKind::kAsyncConciseMethod ||
+         kind == FunctionKind::kArrowGeneratorFunction;
 }