android-切换上下文后，driver.source数据结构由json-变为xml

• Macaca Version:2.0.9

• Macaca Doctor Logs: macaca-doctor version: 2.0.2

  Node.js checklist:

  node env: /usr/local/bin/node node version: v6.10.2

  iOS checklist:

  Xcode Command Line Tools is ready, version: 2347. xcodebuild version: 8.3.3 iproxy[usbmuxd] is installed at: /usr/local/bin/iproxy ios_webkit_debug_proxy is installed at: /usr/local/bin/ios_webkit_debug_proxy carthage is installed, version: 0.23.0

  Android checklist:

  JAVA version is 1.8.0_121 JAVA_HOME is set to /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home ANDROID_HOME is set to /Users/joko/Library/Android/sdk Platforms is set to /Users/joko/Library/Android/sdk/platforms/android-25 ADB tool is set to /Users/joko/Library/Android/sdk/platform-tools/adb gradle is installed, version: 3.5

  Installed driver list:

  android: 2.0.36 electron: 1.1.6 [out-of-date] ios: 2.0.23 [out-of-date]

• Operate System: mac os 10.12.5

• Programming Language: python 2.7

预置环境:android 5.0 webview版本：54.0.2840.85 步骤：切换上下文到webview。然后再切回到native。此时调用driver.source。查看driver.source数据结构 问题描述：此时数据结构类型是xml。再未执行切换到webview->native步骤前，driver.source数据结构是json，请帮忙修复此问题