DimLayer: More release fixes.

DimState and DimAnimatable are sharing ownership of the Dim layer with
either having the possibility to remove it. They aren't holding references
to eachother so its not clear where to consolidate ownership. We take the easy
way out and add some valid checks so they can safely share ownership.

Bug: 130315011
Test: Existing tests pass
Change-Id: Id473e40c58f1ca0f4a6a23284e220c6fd2ec36d2