pixmap erase fast-path

Brian and I saw a measurable speedup on software path rendering when
calling memset(..., 0, ...) instead of looping over one memset per
scanline.  This brings that fast path to the masses.

Change-Id: I792416e30e924efdd6ab40d445148b5c59f7bc62
Reviewed-on: https://skia-review.googlesource.com/41847
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed