Steps to reproduce:
1. Open user provided native Android application project on Android Studio
2. Build & Run to a device
3. Press "Hello World" button, wait until embeded Unity app loads
4. Press the back button, repeat from step 3 if the app does not crash

Expected result: Application.Unload() should not cause application to crash

Reproduced in: 2019.1.0a6, 2018.3.0b6 with .NET 4.6 and .NET 3.5

Tested devices:
Repro:
VLNQA00137, Samsung Galaxy S9+ (SM-G965F), Android 8.0.0, CPU: Exynos 9 Series 9810, GPU: Mali-G72
VLNQA00155, Meizu PRO 7 Plus (PRO 7 Plus), Android 7.0, CPU: MediaTek Helio X30 MT6799, GPU: PowerVR Rogue Marlowe
VLNQA00001, Google Pixel 2 (Pixel 2), Android 8.1.0, CPU: Snapdragon 835 MSM8998, GPU: Adreno (TM) 540
No repro:
VLNQA00093, Samsung Galaxy S6 edge (SM-G925F), Android 7.0, CPU: Exynos 7 Octa 7420, GPU: Mali-T760
VLNQA00028, Samsung Galaxy Note4 (SM-N910F), Android 6.0.1, CPU: Snapdragon 805 APQ8084, GPU: Adreno (TM) 420
VLNQA00124, Google Pixel 2 XL (Pixel 2 XL), Android 9, CPU: Snapdragon 835 MSM8998, GPU: Adreno (TM) 540 - notifies that app keeps crashing