Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.17
Broken: version: 2.80 (sub 64), branch: master (modified), commit date: 2019-05-13 14:46, hash: rB1c1e3de0156d
For the Render Viewport Image/Animation commands, the AA level is currently set through the Sampling panel of the Workbench render engine settings.
The two properties there are "Render" and "Viewport". I suggest that the second should be renamed "Viewport Render" to avoid confusion with the interactive viewport AA level set through the new "Viewport Anti-Aliasing" preference.
I'll throw in that it's really weird to have to change your scene renderer to get at the Viewport Render AA value when you aren't explicitly using the Workbench renderer. In fact, you might just switch the scene renderer to Workbench just to access this parameter, then change it back to Eevee or whatever before even doing the Render Viewport command. It feels like this parameter should either be a Preference as Viewport AA now explicitly is, or it should be a property of the Workspace or something like that.