[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 294dfdca643a0faf296c67ed6270b476db157703..5da096b82467c491be635581813bfd18a8db8ee9 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6846,6 +6846,13 @@ 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)