Pass pack state arguments instead of split parameters. Similar to unpack state, the PixelPackState struct encapsulates all the parameters related to pixel pack buffers. Passing the packstate makes functions more consise. BUG=angle:511 Change-Id: If6954a5085e9b8f828cfc8892a73e7c7514b0c8a Reviewed-on: https://chromium-review.googlesource.com/191032 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>