It is very difficult to implement a truly robust context which includes the graphics reset notification. It requires operating system support which doesn't really exist. Implementations that expose the extension may not actually provide accurate information. Further, several current WebGL implementations actually aren't using OpenGL on Windows (despite all the hubbub), but they're using ANGLE, which is an OpenGL-ES 2.0 to D3D9 translator. Browsers would have to actually use OpenGL in order to take advantage of the ARB_robustness extension. Even if we implemented it, would anybody actually use it and would it provide benefit to the end user? We're still evaluating those questions. In all likelihood, we will implement some form of the extension, but we have no immediate plans to support it at this time.
For our upcoming Fusion hardware and discrete GPUs we are looking at QoS mechanisms, at least for compute workloads. Hopefully, we can leverage some of that work for OpenGL. We'll keep you posted.