add Load2() to Sk4f

and test it.

Change-Id: Ib0c2cf93c63d8d3c36a7d4d60bbec4ecede29bc7
Reviewed-on: https://skia-review.googlesource.com/78480
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
4 files changed