This adds a new "nop" driver that does nothing. This can be selected at
runtime either with the COGL_DRIVER=nop environment variable or by
passing COGL_DRIVER_NOP to cogl_renderer_set_driver()
Adding the nop driver gives us a way to test workloads without any
driver and hardware overheads which can help us understand how Cogl's
state tracking performs in isolation.
Having a nop driver can also serve as an shell/outline for creating
other drivers later.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 90587418233b6438290741d80aedf193ae660cad)
