create imagepriv and name params

Named all parameters and made the names consistent
for documentation.

Moved SK_IMAGEFILTER_UNFLATTEN_COMMON to private file.

TBR=reed@google.com
Bug: skia:6898
Change-Id: I1343d2b16d4217088fa3bc9c40f1f4177fa32740
Reviewed-on: https://skia-review.googlesource.com/66521
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
25 files changed