Bug 1082530, part 1 - Mark DrawTarget::GetUserData as const. r=mattwoodrow
Bug 1082530, part 2 - Fix up Moz2D's UserToDevicePixelSnapped to be more like gfxContext::UserToDevicePixelSnapped, and add a temporary variant to aid in porting. r=mattwoodrow
Bug 1082530, part 3 - Get rid of gfxContext::FLAG_DISABLE_SNAPPING and use DrawTarget UserData to store information on whether to disable pixel snapping. r=mattwoodrow
Bug 1082530, part 4 - Make BasicColorLayer use the variant of Moz2D's UserToDevicePixelSnapped that honors disabling of pixel snapping and make it ignore scaling in the matrix (restore the pre-bug 989858 beharior). r=mattwoodrow
Bug 1082530, part 5 - remove the variant of Moz2D's UserToDevicePixelSnapped that takes a Matrix argument instead of a DrawTarget argument. r=mattwoodrow