message: protect access to ResumptionDataJson during state save
diff: @@ -480,6 +480,9 @@ bool ResumptionDataJson::DropAppDataResumption(const std::string& device_id,
  }
  void ResumptionDataJson::Persist() {
  + // We lock the resumption data because SaveStateToFileSystem accesses
  + // the same dictionary that we use here in ResumptionDataJson
  + sync_primitives::AutoLock autolock(resumption_lock_);
  last_state().SaveStateToFileSystem();
  }
  