Basic shell class for RenderPass

Bug b/119620965

Change-Id: Ice98943587f363f8cf03eddd3cc4c504b899d682
Reviewed-on: https://swiftshader-review.googlesource.com/c/22612Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>