react native webview 添加header 失效？

<WebView
              source={{uri:url,
              headers:{'xxx':'content'}}}//失效不起作用
          />

版本信息如下：

Environment:
  OS: macOS Sierra 10.12.6
  Node: 9.11.1
  Yarn: 1.5.1
  npm: 5.6.0
  Watchman: 4.9.0
  Xcode: Xcode 9.2 Build version 9C40b
  Android Studio: 3.0 AI-171.4443003

Packages: (wanted => installed)
  react: ^16.3.0-alpha.1 => 16.3.1
  react-native: 0.54.2 => 0.54.2

求解答！