[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 d0664a1ff1d8a4cd15cd46532226fe7c66a3cb6b..c2f03a07339d2ca340b8baffad36ba070c81f890 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -1024,7 +1024,7 @@ 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);