Where is the IBuffer byte[].AsBuffer extension method?

During build they mentioned that to get an IBuffer, there's an extension method on byte arrays called AsBuffer(). Unfortunately they didn't mention what namespace it's hiding in, and doesn't seem to be in the many I've adde开发者_开发问答d. Has anyone found where it's hiding at?

The namespace is System.Runtime.InteropServices.WindowsRuntime.

VS Object Browser is your friend here - just be sure to set the framework switcher accordingly. For .NET libraries available in Metro apps, you want ".NET Framework Core 4.5".