[weakrefs] Fix [[KeptObjects]] assertion for only when a microtask checkpoint is performed

Bug: chromium:1073263
Change-Id: I5c054e34242a91dafd6788814a39e97075d1035d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2160019Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67319}

src/api/api.cc

@@ -328,6 +328,7 @@ class CallDepthScope {
   bool CheckKeptObjectsClearedAfterMicrotaskCheckpoint(
       i::MicrotaskQueue* microtask_queue) {
     bool did_perform_microtask_checkpoint =
+        isolate_->thread_local_top()->CallDepthIsZero() &&
         do_callback && microtask_queue &&
         microtask_queue->microtasks_policy() == MicrotasksPolicy::kAuto;
     return !did_perform_microtask_checkpoint ||

test/mjsunit/harmony/weakrefs/clearkeptobjects-on-quit.js

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-weak-refs
+
+// A newly created WeakRef is kept alive until the end of the next microtask
+// checkpoint. V8 asserts that the kept objects list is cleared at the end of
+// microtask checkpoints when the microtask policy is auto. Test that d8, which
+// uses the auto policy, upholds the assert when manually quitting.
+let obj = {};
+let wr = new WeakRef(obj);
+testRunner.quit();