Steps:
1. Open attached project (or download from Asset Store https://www.assetstore.unity3d.com/en/#!/content/22817)
2. Open 'Elements Preview' scene
3. Build setting. Switch to WebGL
4. Player Settings: WebGL memory size 1024 , Enable exceptions : Full
5. Build and Run for WebGL
6. Click on the slider in the scene to set some value
==>
MissingMethodException: Method not found. Default constructor not found 'UnityEngine.SliderState'

Repro in Version 2017.2.0b1 (1a1b26354326)
Not repro in Version 2017.1.0f3 (472613c02cf7)