WebRequestclasses is not supported.
WebRequestclasses is limited.
It is recommended to minimize your references to external libraries, because 1 MB of .NET CIL code roughly translates to 3–4 MB of ARM code. For example, if your application references System.dll and System.Xml.dll then it means additional 6 MB of ARM code if stripping is not used. At some point the application will reach this limit and the linker will have trouble linking the code.