Steps to reproduce:
1. Open attached project
2. Open "Main" scene
3. Open profiler and select CPU usage section
4. Click "L" button to load the AssetBundle
5. Click "U" to unload the AssetBundle
- Inspect the profiler when unloading happened

Result: Unloading an AssetBundle that contains a material causes a call to FindObjectsOfType()
Problem: This could cause performance issues, especially with very large scenes with many objects
Expected result: The functionality of unloading AssetBundles should be optimised because calling FindObjectsOfType() would cause performance issues on large scenes.

Reproduced with: 5.6.2p4, 2017.1.0p1, 2017.2.0b3, 2017.3.0a1