add colorspace param to textblobdiff canvas

Bug: skia:8773
Change-Id: Ib5d04e02a1568ad8a2b3f1baccb9544515f772f9
Reviewed-on: https://skia-review.googlesource.com/c/193373
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Reed <reed@google.com>
6 files changed