Update baseline GM images

This updates the multipicturedraw_* GM images for:

Reduce overdraw in MultiPictureDraw Sierpinski GM - https://codereview.chromium.org/582633003/
Don't turn on dither for saveLayers which have no paint - https://codereview.chromium.org/619363002/

TBR=reed@google.com
NOTRY=true

Review URL: https://codereview.chromium.org/632703003
43 files changed