[canvaskit] Make gm test wrapper not omit known pngs
[canvaskit] Make gm test wrapper not omit known pngs

We just make a global set of known png digests and expect that the test
harness will load this with the appropriate data.

Bug: skia:10812
Change-Id: I8e1fc987d36cc57386167410514803f8c3b90a69
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/328379
Reviewed-by: Chris Dalton <ef7fc3a08ada7d31f16e9a18b5f3c728256e041e@google.com>

aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia