Using ui::TouchEvent makes scroll / pinch gestures coarse

The lifetime of a touch event in Oxide before we pass it to Chromium is:

QTouchEvent -> ui::TouchEvent -> ui::MotionEvent.

Touch co-ordinates are in device independent pixels, and Qt provides these as floats. The constructor for ui::TouchEvent requires us to round the co-ordinates to the nearest integer because it takes a gfx::Point.

This causes a problem - it means that the smallest touch point movement is 1 device-independent pixel, which could be 2 or 3 physical pixels depending on the device scale. This makes scrolling and pinch-zooming appear coarse compared to Chrome/Android (where it's possible to scroll by single physical pixels).

As ui::MotionEvent works with floats, I suggest we just cut out the middleman here and stop using ui::TouchEvent entirely.