Shader _Time value isn't updated when there isn't a Camera in the Scene.

When you don't have a camera in the scene, just a Canvas set to Overlay, the shader animation (via shader code with _Time property) doesn't work. If you switch off Main Camera game object in testScene and close Scene View, leaving just Game View, and then hit Play, effect in Canvas will not be updated.

To repro:
1) Open attached project
2) Open testScene
3) Deactivate main camera game object and close Scene View tab
4) Enter playmode and see the shader animation (uses _Time) not playing on UI graphic
5) Activate camera game object and see animation working.

Reproduced in 5.3.8f1, 5.6.2p4, 2017.2.0b1.