Repeating SkBitmapProcState rounding bias

Observe the bias in repeat matrix procs also.

Introduce a utility class to handle device space -> bitmap space
mapping.

BUG=skia:4680,skia:4649
R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1529833003

Review URL: https://codereview.chromium.org/1529833003