I switched from GapDebug to Crosswalk remote debugging. Everything is fine with exception of 'screencast' in Developer Tools, which is blinking with 5 fps (when I use Crosswalk).
If I switch to 'Elements' tab and move mouse over any DOM element (make it active), the blinking stops. With GapDebug I had no issue. It was nice to ignore physical device and debug app on a computer screen.
May be someone faced similar issue before, thanks