Buffer four scanlines prior to blitting. We will eventually use this
to blit four scanlines in a row in order to aggressively compress alpha
masks as the information comes in. This CL is only to introduce the API
and to make sure that nothing breaks in the general case.

R=reed@google.com, robertphillips@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/387953005
2 files changed