Use shared toSRGBD50 matrix in SkPngCodec

BUG=skia:

Change-Id: I1d2629ef954d8ac7211cfbb4707125ed175af63c
Reviewed-on: https://skia-review.googlesource.com/6553
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed