remove use of initial matrix

This was just wrong. It should be determine perspective
using the matrix that we are drawing with, and not the initial
matrix.

Change-Id: I8410ced714d2c766305656bdbd797f9dea59b71e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/339796
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
4 files changed