message: Add gl_context method to Headless
diff: @@ -5,7 +5,7 @@ use crate::debug;
  use crate::context;
  use crate::backend::{self, Backend};
  use std::rc::Rc;
  -use std::cell::RefCell;
  +use std::cell::{Ref, RefCell};
  use std::ops::Deref;
  use std::os::raw::c_void;
  use super::glutin;
  @@ -120,6 +120,11 @@ impl Headless {
  Ok(Headless { context, glutin: glutin_context })
  }
  + /// Borrow the inner glutin context
  + pub fn gl_context(&self) -> Ref<'_, Takeable<glutin::Context<Pc>>> {
  + self.glutin.borrow()
  + }
  +
  /// Start drawing on the backbuffer.
  ///
  /// This function returns a `Frame`, which can be used to draw on it. When the `Frame` is
  