message: Call flush() after writing a log message to a file.
  Without flush(), the messages are not logged in the file promptly.
  So if the process crashes, only truncated messages are logged.
diff: @@ -237,6 +237,7 @@ void LogStreamImpl::Write(LogSeverity severity, const std::string &log) {
  // triggered |LOG(ERROR)|.
  if (real_log_stream_) {
  *real_log_stream_ << log;
  + real_log_stream_->flush();
  }
  #endif // OS_ANDROID
  }
  