Add callback function to allow resize messages to be sent on mac.

src/win32/mod.rs

@@ -46,6 +46,9 @@ impl HeadlessContext {
     pub fn get_api(&self) -> ::Api {
         ::Api::OpenGl
     }
+
+    pub fn set_window_resize_callback(&mut self, _: fn(uint, uint)) {
+    }
 }
 
 /// The Win32 implementation of the main `Window` object.
@@ -276,6 +279,9 @@ impl Window {
     pub fn get_api(&self) -> ::Api {
         ::Api::OpenGl
     }
+
+    pub fn set_window_resize_callback(&mut self, _: fn(uint, uint)) {
+    }
 }
 
 #[unsafe_destructor]