@Override
  public String toString() {
    if (mSerializedChainString == null) {
      mSerializedChainString = getNodeString();
      if (mParent != null) {
        mSerializedChainString = mParent.toString() + PARENT_SEPARATOR + mSerializedChainString;
      }
    }
    return mSerializedChainString;
  }
Get the top level context chain, which can be the current context chain itself.
fbcore/src/main/java/com/facebook/common/callercontext/ContextChain.java