Outset texture coordinates similarly to positions in GrTextureOp

Previously we inverted a matrix to compute a mapping from positions
to teture coords and applied it to the outset positions.

Change-Id: I164d827caa2cebcf690290ff1a3f2859a8c285b3
Reviewed-on: https://skia-review.googlesource.com/c/161831
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
2 files changed