drm_hwcomposer: Add glworker

The glworker allows signalling the fence synchronously once the GL
work is done. It also helps performance by putting all GL in a
separate thread, which avoids (costly on some GPUs) makecurrent.

Change-Id: Ia4ee137df5c9a4b1afcf6180407371d6ba7f699a
diff --git a/gl_compositor.h b/gl_compositor.h
index 528d8ac..450ca67 100644
--- a/gl_compositor.h
+++ b/gl_compositor.h
@@ -48,7 +48,7 @@
   int BeginContext();
   int EndContext();
   int GenerateShaders();
-  int DoComposition(const GLComposition &composition);
+  int DoComposition(GLComposition *composition);
   int DoFenceWait(int acquireFenceFd);
   int CreateTextureFromHandle(buffer_handle_t handle,
                               struct texture_from_handle *tex);