To reproduce:

1. Download attached project "Test2018-2.zip" and open in Unity
2. Open "SampleScene" scene
3. Set Android platform
4. Assign the icon "icontest" in PlayerSettings in Default Icon, Adaptive Icon, Round Icon and Legacy Icon
5. Build and run the project on an Android device
6. Check how Icon looks like
7. Observe that the borders of Icon are not visible at all

Notes:
- This issue is reproducible only on Android devices
- This issue is not reproducible in iOS devices
- This issue is not reproducible in Windows and OSX Standalones
- In the attached picture you will see how icons look like in 2017.4 and 2018.* - Test2017 has the normal Icon and Test2018 has a zoomed in Icon

Devices:
- Google Pixel 2, OS: 8.1.0, CPU: arm64-v8a, GPU: Adreno (TM) 540 - Reproduced
- Samsung Galaxy S9, OS: 8.0.0, CPU: arm64-v8a, GPU: Mali-G72 - Reproduced
- iPhone 7, iOS: 11.2.6, CPU: A10 - Not Reproduced

Reproduced on Unity 2018.1.0a5, 2018.1.9f1, 2018.2.3f1, 2018.2.1f1 and 2018.3.0a9
Not reproduced on Unity 2017.4.9f1 and 2018.1.0a4
Regression on Unity 2018.1.0a5