Add IsTransitionable FFI

components/style/gecko/generated/bindings.rs

@@ -2248,6 +2248,9 @@ extern "C" {
 extern "C" {
     pub fn Servo_Property_IsAnimatable(property: nsCSSPropertyID) -> bool;
 }
+extern "C" {
+    pub fn Servo_Property_IsTransitionable(property: nsCSSPropertyID) -> bool;
+}
 extern "C" {
     pub fn Servo_Property_IsDiscreteAnimatable(property: nsCSSPropertyID)
      -> bool;

components/style/properties/helpers/animated_properties.mako.rs

@@ -338,6 +338,19 @@ impl From<nsCSSPropertyID> for TransitionProperty {
     }
 }
 
+/// Returns true if this nsCSSPropertyID is one of the transitionable properties.
+#[cfg(feature = "gecko")]
+pub fn nscsspropertyid_is_transitionable(property: nsCSSPropertyID) -> bool {
+    match property {
+        % for prop in data.longhands + data.shorthands_except_all():
+            % if prop.transitionable:
+                ${helpers.to_nscsspropertyid(prop.ident)} => true,
+            % endif
+        % endfor
+        _ => false
+    }
+}
+
 /// An animated property interpolation between two computed values for that
 /// property.
 #[derive(Clone, Debug, PartialEq)]

ports/geckolib/glue.rs

@@ -702,6 +702,12 @@ pub extern "C" fn Servo_Property_IsAnimatable(property: nsCSSPropertyID) -> bool
     animated_properties::nscsspropertyid_is_animatable(property)
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_Property_IsTransitionable(property: nsCSSPropertyID) -> bool {
+    use style::properties::animated_properties;
+    animated_properties::nscsspropertyid_is_transitionable(property)
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_Property_IsDiscreteAnimatable(property: nsCSSPropertyID) -> bool {
     match AnimatableLonghand::from_nscsspropertyid(property) {