Add simple test for dragend workaround.
The work-around added to the build relation 'dragend' event handler to prevent
the serviceClick handler from processing and doing the wrong thing is now
tested. An integration test using simulated drags and a click on the service
didn't prove feasible so this unit test is used.
R=benji, gary.poster
CC=
https://codereview.appspot.com/7237053