Use WindowMethods to get native graphics metadata instead of
relying on azure. This is a prerequisite for the switch to glutin.

Tested on Linux, mac. Tested that android + cef build.
auto merge of #3800 : glennw/servo/native-gfx-metadata, r=mbrubeck

This is a prerequisite for glutin support.

Tested on Linux, mac. Tested that android + cef build.