add win subclass of raster-allocator

BUG=skia:

Change-Id: Ibe1664b599a88dce06d03cf8eea10db5f75ce037
Reviewed-on: https://skia-review.googlesource.com/6924
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed