[esnext] prototype runtime implementation for async functions

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index 707da746c19da72bc7923afd473725eb701e7997..720a5ade0d87c29f6b9c0a02f27b9dd603d8fdb4 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -1023,7 +1023,7 @@ class FastNewClosureStub : public HydrogenCodeStub {
  private:
   STATIC_ASSERT(LANGUAGE_END == 3);
   class LanguageModeBits : public BitField<LanguageMode, 0, 2> {};
-  class FunctionKindBits : public BitField<FunctionKind, 2, 8> {};
+  class FunctionKindBits : public BitField<FunctionKind, 2, 9> {};
 
   DEFINE_CALL_INTERFACE_DESCRIPTOR(FastNewClosure);
   DEFINE_HYDROGEN_CODE_STUB(FastNewClosure, HydrogenCodeStub);