Scrolling is broken on Android

[larsbergstrom]

I saw clicking on a link work once, but scrolling and pinch-zoom appear to be non-functional.

[mbrubeck]

Glutin translates touch input on Android into mouse events. Upstream Glutin master has a touch event API, but this isn't yet used in the Android port.

We could easily change Servo's android port to make "mouse" movement scroll the page instead of sending DOM mouse events, but this would break the demos that use mousemove events for other purposes.

To make touch input usable for both scrolling and DOM events, we need to implement the Touch Events DOM API, and cancel scrolling if the web page calls preventDefault on the "touchstart" or "touchmove" event.

[mbrubeck]

If a temporary hack is needed for demo purposes, we could also provide a way for a web page to opt out of touch scrolling, for example by implementing a tiny subset of the 'touch-action' CSS property.

[mbrubeck]

I started working on basic touch event support at https://github.com/mbrubeck/servo/commits/touchevent

[waddlesplash]

#7204 was merged.