Context
When native clients load articles via mobile-html, they need to be able to adjust the font size.

Proposed solution
Provide a function to set a text size adjustment percentage:
setTextSizeAdjustmentPercentage(textSizeAdjustmentPercentage)

Notes
This is currently mainly needed by the iOS app. iOS currently sets -webkit-text-size-adjust to a percentage value, e.g. 100% as a style of the body element. We should probably also consider setting text-size-adjust as well.

from iOS code: document.body.style['-webkit-text-size-adjust'] = textSize

This is the lower level transformation in the page library. A similar function should be exposed in the abstraction layer, but with a callback.
We should also consider adding an input field for the text size adjustment to the AllTransforms demo.