In play mode, memory usage constantly increases after using UI canvas at runtime. Even if no tasks are performed, memory consumption keeps increasing at idling.

Steps for reproduction:
1) Download the project below and open the scene `Mixed_Area`
2) Enter play mode
3) Open Task Manager
4) Use the UI buttons located at the bottom of the screen (there are buttons called as Directional, Spotlight, Point and Area)
5) Keep switching between the scenes through UI buttons until memory usage is higher than ~550 MB.
6) Once you reach that memory consumption level, stop performing any tasks in the editor
7) Observe that even when idling, memory consumption keeps increasing (image shared below as `MemoryIncreasing`)

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Besides the project attached to the case, the project from case 790887 (link shared in comments section) also demonstrates a performance regression in the profiler. Steps to reproduce the issue on that project:

1) After downloading the project, open the scene `start`
2) Open the profiler and enter play mode
2) In the game view, press on `Load Scene with Lighting Data` button
3) Observe the huge spike and the time it takes to load the scene (image shared below as `ProfilerLoadTime`)

Notes:
- It's a regression, this behaviour is not observed in 5.6.0f3 or 2017.1.0f1. At idling, either memory is deallocated or its usage is stable
- Reproduced in 2017.2.0a2
- Issue is not related to GI loading
- In particular, very high memory usage amounts are observed with the project from case 790887 (up to ~12 GB, image shared below as `MemoryIncreasing`)