Move zoom code to its own file.
diff --git a/src/compositor.h b/src/compositor.h
index 5a52e60..df100d5 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -642,6 +642,8 @@
 weston_text_cursor_position_notify(struct weston_surface *surface,
 						wl_fixed_t x, wl_fixed_t y);
 void
+weston_output_init_zoom(struct weston_output *output);
+void
 weston_output_update_zoom(struct weston_output *output, uint32_t type);
 void
 weston_output_update_matrix(struct weston_output *output);