style: Generate combined transform just once.

Differential Revision: https://phabricator.services.mozilla.com/D18567

components/style/properties/cascade.rs

@@ -629,6 +629,10 @@ impl<'a, 'b: 'a> Cascade<'a, 'b> {

        #[cfg(feature = "gecko")]
        {
            if let Some(display) = builder.get_box_if_mutated() {
                display.generate_combined_transform();
            }

            if let Some(bg) = builder.get_background_if_mutated() {
                bg.fill_arrays();
            }

components/style/properties/gecko.mako.rs

@@ -3023,6 +3023,11 @@ fn static_assert() {
                          will-change shape-outside contain touch-action
                          translate scale""" %>
<%self:impl_trait style_struct_name="Box" skip_longhands="${skip_box_longhands}">
    #[inline]
    pub fn generate_combined_transform(&mut self) {
        unsafe { bindings::Gecko_StyleDisplay_GenerateCombinedTransform(&mut self.gecko) };
    }

    #[inline]
    pub fn set_display(&mut self, v: longhands::display::computed_value::T) {
        self.gecko.mDisplay = v;