exo: Add Surface::SetBufferScale.

components/exo/wayland/server.cc

Index: components/exo/wayland/server.cc
diff --git a/components/exo/wayland/server.cc b/components/exo/wayland/server.cc
index 2bb39324cb8fb79b7451d1165594c93a1059382b..18dc3826e9f528f2c6c52bc97c61fd4905a2808a 100644
--- a/components/exo/wayland/server.cc
+++ b/components/exo/wayland/server.cc
@@ -175,7 +175,15 @@ void surface_set_buffer_transform(wl_client* client,
 void surface_set_buffer_scale(wl_client* client,
                               wl_resource* resource,
                               int32_t scale) {
-  NOTIMPLEMENTED();
+  if (scale < 1) {
+    wl_resource_post_error(resource, WL_SURFACE_ERROR_INVALID_SCALE,
+                           "buffer scale must be at least one "
+                           "('%d' specified)",
+                           scale);
+    return;
+  }
+
+  GetUserDataAs<Surface>(resource)->SetBufferScale(scale);
 }
 
 const struct wl_surface_interface surface_implementation = {