Get should be a const method.
Get should be a const method.

Otherwise, the returned handler_ can still be modified.

Change-Id: I59dea4aa5284f7154d3c096556e6e497890c26ca

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst