Why can't I create a new Camera.Size object?

In a test fixture I am trying to create a mock Android.Hardware.Camera.Size object like this:

var test = new Android.Hardware.Camera.Size(12, 10);

But I get the following compiler error:

Cannot access protected member 'Android.Hardware.Camera.Size.Size(System.IntPtr, Android.Runtime.JniHandleOwnership)' via a qualifier of type `Android.Hardware.Camera.Size'. The qualifier must be of type 'TestCtrlz.TestsSample' or derived from it