Reproduction steps:
1. Download project "NavMeshApiDemoLarge.zip" and open in Unity
2. Chose scene "GenerationBug"
3. Select Window -> Profiler -> Memory
4. Enter Play mode
5. In Game view move forward (press "W" + shift) for 10 - 15 seconds

Expected: memory should be freed after GameObject.Destroy() is used (InfiniteTerrain.cs) when distance between mesh and player is further than 700
Actual: memory allocation increases and Game view becomes laggy or Unity crashes

Reproduced: 5.5.4p2; 5.6.3p2; 2017.1.0p5; 2017.2.0b9; 2017.3.0a6

Note: Unity crashes on versions 2017.1.0b2 - 2017.1.0f3 (Error.png) and after some time Meshes allocated memory becomes Unknown in Unity 5.5.4p2 (5.5.4p2 Unity.png)