Fast Pinch-Zoom support on the sizer.

This patch adds a new class ZoomHelper that
is used to control the zooming of the document
by API and/or touch gestures. CSS3D transforms
are used to do extremely fast bitmap scaling
of the sizer.

The browser will only update the scroll dimensions
of the container if the 'float' of the sizer is toggled
to 'none'and then 'left'.