message: Remove frame->f_trace DCHECK, which is not always nullptr.
diff: @@ -50,7 +50,6 @@ class StackTrace final {
  int i = 0;
  for (; i < kMaxDepth && frame != nullptr; frame = frame->f_back, ++i) {
  PyCodeObject* code_obj = frame->f_code;
  - DCHECK(frame->f_trace == nullptr);
  DCHECK(code_obj != nullptr);
  Py_INCREF(code_obj);
  