Breaking this out of #8410.

Based on http://bit.ly/flutter-adaptive-widget-problem, there isn't clear feedback on how we can auto-adapt widgets in a generic sense.

Branching off type 4, simple 1:1 matchings off to this bug for tracking.

Switching candidates:

• Scrollbar/CupertinoScrollbar ⇒ Scrollbar.adaptive
• Slider/CupertinoSlider ⇒ Slider.adaptive
• Switch/CupertinoSwitch ⇒ Switch.adaptive
• CircularProgressIndicator/CupertinoActivityIndicator ⇒ CircularProgressIndicator.adaptive
• TextField/CupertinoTextField
• FlatButton/CupertinoButton & RaisedButton/CupertinoButton.fill()