Delegated renderer: Share context support for QNX

Add code to extract the EGL context on QNX for use as the share context
in the Chromium GPU process/thread. Very similar to the other
platforms.

Change-Id: I54fba69283e984a392c11922da2483ce921ea594
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>