WIP [esnext] implement async iteration proposal

src/code-stub-assembler.h

Index: src/code-stub-assembler.h
diff --git a/src/code-stub-assembler.h b/src/code-stub-assembler.h
index 77066b2bd0a46bb2a1d147c5135e5f13b82d521e..3f98b1c94c4de2b766bb041b12e1e385ae802b0e 100644
--- a/src/code-stub-assembler.h
+++ b/src/code-stub-assembler.h
@@ -554,6 +554,11 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
 
   Node* AllocateJSArrayIterator(Node* array, Node* array_map, Node* map);
 
+  Node* AllocateJSIteratorResult(Node* context, Node* value, Node* done);
+  Node* AllocateJSIteratorResult(Node* context, Node* value, bool done) {
+    return AllocateJSIteratorResult(context, value, BooleanConstant(done));
+  }
+
   void FillFixedArrayWithValue(ElementsKind kind, Node* array, Node* from_index,
                                Node* to_index,
                                Heap::RootListIndex value_root_index,
@@ -1133,6 +1138,31 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   // Debug helpers
   Node* IsDebugActive();
 
+  // Useful tools for PrintF-style debugging CSA builtins.
+  void ReleasePrint(const char* c_str) {
+    std::string std_str(c_str);
+    std_str += '\n';
+    Handle<String> str =
+        factory()->NewStringFromAsciiChecked(std_str.c_str(), TENURED);
+    CallRuntime(Runtime::kGlobalPrint, NoContextConstant(), HeapConstant(str));
+  }
+
+  void ReleaseDebugPrint(Node* object) {
+    CallRuntime(Runtime::kDebugPrint, NoContextConstant(), object);
+  }
+
+  void Print(const char* c_str) {
+#ifdef DEBUG
+    ReleasePrint(c_str);
+#endif
+  }
+
+  void DebugPrint(Node* object) {
+#ifdef DEBUG
+    ReleaseDebugPrint(object);
+#endif
+  }
+
   // TypedArray/ArrayBuffer helpers
   Node* IsDetachedBuffer(Node* buffer);