Break SkTestCanvas.cpp off into own file list to put only in GPU builds

This will hopefully fix the Android roll.

Change-Id: Id49b4bfce9929fd2870dadd8c8cb2923346a6e4b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/714642
Reviewed-by: Ben Wagner <bungeman@google.com>
4 files changed