take screenshot in chrome device emulator mode
found this menu, which take screenshot of device screen only
latest chrome have "Capture full size screenshot" 
in latest chrome we can capture node ,
- open developer tool
- select node to be capture
- press CMD/CTRL + SHIFT + P, it will open a "command menu"
- filter commands using "screenshot" keyword
- choose "capture node screenshot"
more info at https://developers.google.com/web/updates/2017/08/devtools-release-notes