mousearea: add areaId refer count

tower: https://tower.im/projects/15081ba156b14fa4bd6d9e82f91edff3/todos/0775bcda4224419d9354cb307abde19d/#3ec7351ad8db4d3c8387ca5212543406

Change-Id: I4f347c98c20856f71427c0c1be65852e30bb09a9