-e: see title, some errors are thrown when running the build
--works well with old .NET 3.5
--works for iOS build with .NET 4.6
--disabling stripping doesn't change the behaviour

-repro:
--get Standard Assets from A$
--switch to .NET 4.6
--build for WebGL
--run build
--NOTICE you are missing the UI in the top right corner and several errors are logged in the browser console:
---Rethrow as TypeInitializationException: The type initializer for 'UnityEngine.UI.Graphic' threw an exception.
---MissingMethodException: Default constructor not found for type System.Collections.Generic.List`1[[UnityEngine.Canvas, UnityEngine, Version=0.0.0.0, Culture=, PublicKeyToken=null]]
--Thrown on each click in the scene:
---MissingMethodException: Default constructor not found for type System.Collections.Generic.List`1[[UnityEngine.EventSystems.IEventSystemHandler, UnityEngine.UI, Version=1.0.0.0, Culture=, PublicKeyToken=null]]