To reproduce:

1. Create a new project
2. Create new GUI Skin
3. Drag new GUI Skin into the Hierarchy
4. Select the new object in the Hierarchy
5. (Optional) Enter Play mode

Expected: GUI Skin cannot be dragged into the Hierarchy
Actual: it is possible to drag GUI Skin into the Hierarchy, this way the new game object with Playable Director component is created and the GUI Skin is assigned to Playable property. Entering Play mode with this setup causes the Editor to crash.

Reproduced in 2017.1.0a5, 2017.1.0f1, 2017.1.0f2, 2017.2.0b1
Did not reproduce in 5.5.2f1, 5.6.2f1, 2017.1.0a4