UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.110 Safari/537.36

Steps to reproduce the problem:
In our overridden pp::Instance function we do the following:

    ...
    const int32_t attrib_list[] = {
            PP_GRAPHICS3DATTRIB_ALPHA_SIZE, 0,
            PP_GRAPHICS3DATTRIB_DEPTH_SIZE, 24,
            PP_GRAPHICS3DATTRIB_SAMPLES, 2,
            PP_GRAPHICS3DATTRIB_SAMPLE_BUFFERS, 1,
            PP_GRAPHICS3DATTRIB_NONE
    };

    context = pp::Graphics3D(this, attrib_list);
    ...

This has been creating a non null context since development began for us 18 months ago.
Since Version 58.0.3029.33 beta (64-bit) on Windows we have been getting a null context.

By reducing the attribute list to:

    ...
    const int32_t attrib_list[] = {
            PP_GRAPHICS3DATTRIB_ALPHA_SIZE, 0,
            PP_GRAPHICS3DATTRIB_DEPTH_SIZE, 24,
            PP_GRAPHICS3DATTRIB_NONE
    };

    context = pp::Graphics3D(this, attrib_list);
    ...

We are able to get a non null context but with reduced image quality.

What is the expected behavior?
We would like to be able to use multi sampling on browsers that were previously able to use multi sampling.
We would like to know if this is a new bug in the Beta release or a change in behaviour that will be in newer chrome releases.

What went wrong?
We are no longer able to use multi sampling on browsers that previously supported it

Did this work before? Yes Version 57.0.2987.133 (64-bit)

Does this work in other browsers? Yes

Chrome version: 58.0.3029.33  Channel: beta
OS Version: 10
Flash Version: