[esnext] prototype runtime implementation for async functions

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index bace194207694f3789edc00c28c3a44f65f92f13..c03dc24b9c804fadd4aa14b1e3f9b775cf702a6b 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6853,6 +6853,13 @@ class SharedFunctionInfo: public HeapObject {
   // Indicates that this function is a generator.
   DECL_BOOLEAN_ACCESSORS(is_generator)
 
+  // Indicates that this function is an async function.
+  DECL_BOOLEAN_ACCESSORS(is_async)
+
+  // Indicates that this function can be suspended, either via YieldExpressions
+  // or AwaitExpressions.
+  inline bool is_resumable() const;
+
   // Indicates that this function is an arrow function.
   DECL_BOOLEAN_ACCESSORS(is_arrow)