Steps to reproduce:
1. Switch to Android platform
2. Open scene "ItemPackTextures" and press play (!)
3. Open custom editor window "Tools/Material Combiner"
4. Uncheck "DryRun" and press "Combine Materials"
5. Notice the combined texture produced by PackTextures being saved to "Assets/ItemTexture_Combined"
6. Repeat the steps on the Windows or WebGL platform and observe that the size is higher

Expected result: Texture2D.PackTextures should not cap maximumAtlasSize to 4096 on mobile platforms

Reproduced in: 2019.1.0a1, 2018.3.0b8, 2018.2.11f1 on Android, iOS platforms
Does not occur in: 2019.1.0a6, 2019.1.0a2