[promises] Add %WaitForPromise runtime call to allow tests to reliably wait for promises to be fini…

src/runtime/runtime-promise.cc

Index: src/runtime/runtime-promise.cc
diff --git a/src/runtime/runtime-promise.cc b/src/runtime/runtime-promise.cc
index 7f8419940af2640570200c154262513962e80266..b12b7dde1b68f01aa3a3ad63fd3818f65dea93f4 100644
--- a/src/runtime/runtime-promise.cc
+++ b/src/runtime/runtime-promise.cc
@@ -162,14 +162,23 @@ RUNTIME_FUNCTION(Runtime_PromiseHookBefore) {
 RUNTIME_FUNCTION(Runtime_PromiseHookAfter) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
-  CONVERT_ARG_HANDLE_CHECKED(JSObject, promise, 0);
-  if (promise->IsJSPromise()) {
+  CONVERT_ARG_HANDLE_CHECKED(JSObject, arg, 0);
+  if (arg->IsJSPromise()) {
     isolate->RunPromiseHook(PromiseHookType::kAfter,
-                            Handle<JSPromise>::cast(promise),
+                            Handle<JSPromise>::cast(arg),
                             isolate->factory()->undefined_value());
   }
   return isolate->heap()->undefined_value();
 }
 
+RUNTIME_FUNCTION(Runtime_IncrementWaitCount) {
+  isolate->IncrementWaitCount();
+  return isolate->heap()->undefined_value();
+}
+
+RUNTIME_FUNCTION(Runtime_DecrementWaitCount) {
+  isolate->DecrementWaitCount();
+  return isolate->heap()->undefined_value();
+}
 }  // namespace internal
 }  // namespace v8