Don't run the second pass of the pending phantom callbacks if the heap has been torn down.

src/cancelable-task.h

+// Copyright 2015 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.
+
+#ifndef V8_CANCELABLE_TASK_H_
+#define V8_CANCELABLE_TASK_H_
+
+#include "include/v8-platform.h"
+#include "src/base/macros.h"
+
+namespace v8 {
+namespace internal {
+
+class Isolate;
+
+class CancelableTask : public Task {
+ public:
+  explicit CancelableTask(Isolate* isolate);
+  ~CancelableTask() override;
+
+  void Cancel() { is_cancelled_ = true; }
+
+  void Run() final {
+    if (!is_cancelled_) {
+      RunInternal();
+    }
+  }
+
+  virtual void RunInternal() = 0;
+
+ protected:
+  Isolate* isolate_;
+
+ private:
+  bool is_cancelled_;
+
+  DISALLOW_COPY_AND_ASSIGN(CancelableTask);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_CANCELABLE_TASK_H_