Added varying struct

TBR=
BUG=skia:

Review URL: https://codereview.chromium.org/671023002
rebaseline for new shaderproc

BUG=skia:

Review URL: https://codereview.chromium.org/674123003
Add isScale() helper function to SkMatrix44.

This will be used later in Chromium to cleanup gfx::Transform::IsScale2d().

BUG=408710,skia:997
TEST=None
R=bsalomon@google.com,danakj@chromium.org

Review URL: https://codereview.chromium.org/676583002
Revert of Added varying struct (patchset #9 id:160001 of https://codereview.chromium.org/671023002/)

Reason for revert:
may have caused gm change on arm

Original issue's description:
> Added varying struct
>
> TBR=
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/852ae80b9c3c6fd53f993ac35133d80863993cbe

TBR=bsalomon@google.com,joshualitt@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/675193002
add color wheel to validate decoding colors

BUG=skia:3061
R=mtklein@google.com

Review URL: https://codereview.chromium.org/681433002