Bug 1371838 - set the window_id as renderer_id to WR. r=jrmuizel

MozReview-Commit-ID: 7YbQNzTNpmE

gfx/webrender_bindings/src/bindings.rs

@@ -697,6 +697,7 @@ pub extern "C" fn wr_window_new(window_id: WrWindowId,
                 }
             }
         },
+        renderer_id: Some(window_id.0),
         ..Default::default()
     };