[esnext] prototype runtime implementation for async functions

src/builtins.h

Index: src/builtins.h
diff --git a/src/builtins.h b/src/builtins.h
index 44143514111bc4b2bc12e552dad19293abc7f244..d2bb9b58b1ff9c5f4ed7636a62ebefab26ebe9a8 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -114,6 +114,7 @@ inline bool operator&(BuiltinExtraArguments lhs, BuiltinExtraArguments rhs) {
   V(FunctionPrototypeToString, kNone)                          \
                                                                \
   V(GeneratorFunctionConstructor, kTargetAndNewTarget)         \
+  V(AsyncFunctionConstructor, kTargetAndNewTarget)             \
                                                                \
   V(GlobalEval, kTarget)                                       \
                                                                \
@@ -312,6 +313,8 @@ inline bool operator&(BuiltinExtraArguments lhs, BuiltinExtraArguments rhs) {
   V(GeneratorPrototypeNext, 2)    \
   V(GeneratorPrototypeReturn, 2)  \
   V(GeneratorPrototypeThrow, 2)   \
+  V(AsyncFunctionNext, 2)         \
+  V(AsyncFunctionThrow, 2)        \
   V(MathCeil, 2)                  \
   V(MathClz32, 2)                 \
   V(MathFloor, 2)                 \
@@ -635,6 +638,9 @@ class Builtins {
   // ES6 section 25.3.1.4 Generator.prototype.throw ( exception )
   static void Generate_GeneratorPrototypeThrow(CodeStubAssembler* assembler);
 
+  static void Generate_AsyncFunctionNext(CodeStubAssembler* assembler);
+  static void Generate_AsyncFunctionThrow(CodeStubAssembler* assembler);
+
   // ES6 section 19.1.3.2 Object.prototype.hasOwnProperty
   static void Generate_ObjectHasOwnProperty(CodeStubAssembler* assembler);