WIP [esnext] implement async iteration proposal

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index 5ccd40757da07b611c3a1dc12f16bbd0b831109d..79fb98c88c44733544dd570ee45d5310edc4a8d5 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1097,7 +1097,11 @@ enum FunctionKind : uint16_t {
   kClassConstructor =
       kBaseConstructor | kDerivedConstructor | kDefaultConstructor,
   kAsyncArrowFunction = kArrowFunction | kAsyncFunction,
-  kAsyncConciseMethod = kAsyncFunction | kConciseMethod
+  kAsyncConciseMethod = kAsyncFunction | kConciseMethod,
+
+  // https://tc39.github.io/proposal-async-iteration/
+  kAsyncConciseGeneratorMethod = kAsyncFunction | kConciseGeneratorMethod,
+  kAsyncGeneratorFunction = kAsyncFunction | kGeneratorFunction,
 };
 
 inline bool IsValidFunctionKind(FunctionKind kind) {
@@ -1116,7 +1120,9 @@ inline bool IsValidFunctionKind(FunctionKind kind) {
          kind == FunctionKind::kDerivedConstructor ||
          kind == FunctionKind::kAsyncFunction ||
          kind == FunctionKind::kAsyncArrowFunction ||
-         kind == FunctionKind::kAsyncConciseMethod;
+         kind == FunctionKind::kAsyncConciseMethod ||
+         kind == FunctionKind::kAsyncConciseGeneratorMethod ||
+         kind == FunctionKind::kAsyncGeneratorFunction;
 }
 
 
@@ -1141,6 +1147,12 @@ inline bool IsAsyncFunction(FunctionKind kind) {
   return kind & FunctionKind::kAsyncFunction;
 }
 
+inline bool IsAsyncGeneratorFunction(FunctionKind kind) {
+  DCHECK(IsValidFunctionKind(kind));
+  const FunctionKind kMask = FunctionKind::kAsyncGeneratorFunction;
+  return (kind & kMask) == kMask;
+}
+
 inline bool IsResumableFunction(FunctionKind kind) {
   return IsGeneratorFunction(kind) || IsAsyncFunction(kind) || IsModule(kind);
 }