Pass params of shareable type by const-ref rather than by value

...where passing them by value was not intentional.

Change-Id: Ifd5036d57b41fddeeacfbd3f5890881605b80647
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>