Reproduction steps:
1. Open user's attached project ("CEFglue")
2. Enter play mode and inspect the callback output on UI textbox
3. Build and start the game
4. Inspect that there is no callback

Expected: libcef.dll is found both in Editor Playmode and in Game Build
Actual: libcef.dll is not found in Editor, but found in Game Build

Reproduced in: 2017.2.3p2, 2017.4.7f1, 2018.1.9f1, 2018.2.0f2, 2018.3.0a4

Note:
Project cannot be built in Unity 2017.2.3p2, 2017.4.7f1