In service composition view drag and drop a policy onto the canvas. An error is displayed and the UI hangs.

The supported way of adding a policy is to select the "Add Policy" that pops-up when you hover over a policy in the left hand window. 

The most intuitive behavior would be to support dragging and dropping of policies in the same way as other resources. However, at the very least, if we will not support that, an error should be displayed to the user to inform them of the correct way to add a policy.