Paint supports translate, rotate, scale functions for transformation
The origin of these transformation is center of the paint,
thus you have to consider the center-aligned vertices if you'd like to use
these transformation functions.
This policy has been considered for scene transformation.
Change-Id: I78b63d7965faec0ec5b9a98a7776993744534b54
hide engine() interface of shape that's not friendly one by users.
instead canvas would access shape internal data to update/draw it.
Now Paint cannot update itself but has to request to Canvas for it.
Change-Id: Ibafd0864a65c3c33238789d1a3e06c49c4378349
