[usecase-cordova][XWALK-2330] Add usecase for Cordova Screenshot plugin

- Use Cordova Screenshot plugin to capture screenshot of xwalkView
- Fail reason: XWALK-2233

Impacted tests(approved): new 1, update 0, delete 0
Unit test platform: [Android]
Unit test result summary: pass 0, fail 1, block 0
Merge pull request #1069 from haoxli/haoxli/usecase-cordova/add-screenshot

[usecase-cordova][XWALK-2330] Add usecase for Cordova Screenshot plugin