How to reproduce:
1. Open a new Unity project with High-Definition RP template
2. Select Assets/Settings/HDRenderPipelineAsset.asset
3. In the Inspector, change "Reflection Cubemap Size" to 512
4. Change "Probe Cache Size" to 512
5. Move Unity Editor window around

Expected result: Editor does not freeze and crash.
Actual result: Editor freezes, the last step usually results in a crash.

Reproducible with - 2018.1.0b5, 2018.1.9f1, 2018.2.1f1, 2018.3.0a6

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By design: The scene crashes because the project runs out of GPU memory. Unity doesn't have a system to catch this case and it is expected to crash.