Implement DWriteFontTypeface::onGetVariationDesignPosition on win10.

Copy into 'coordinates' (allocated by the caller) the design variation
coordinates. Return the number of axes, or -1 if there is an error.

Change-Id: Ie2fe88aaae358ec471aafd655b4ed0be80d43ae6
Reviewed-on: https://skia-review.googlesource.com/134329
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Bruce Wang <brucewang@google.com>
3 files changed