Use namespaces for context owned objects.

Bug 19219444

Change-Id: I9606dfb30693a15a06896d83888022ccbaa8db2e
Reviewed-on: https://swiftshader-review.googlesource.com/5010
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>