style: make contain-intrinsic-size *animatable*

Differential Revision: https://phabricator.services.mozilla.com/D151231

components/style/properties/longhands/position.mako.rs

@@ -465,7 +465,6 @@ ${helpers.predefined_type(
 )}
 
 % for (size, logical) in ALL_SIZES:
-    // FIXME: Bug 1778296, "contain-intrinsic-*" properties should be animatable.
     ${helpers.predefined_type(
         "contain-intrinsic-" + size,
         "ContainIntrinsicSize",
@@ -475,6 +474,6 @@ ${helpers.predefined_type(
         logical=logical,
         gecko_pref="layout.css.contain-intrinsic-size.enabled",
         spec="https://drafts.csswg.org/css-sizing-4/#intrinsic-size-override",
-        animation_value_type="none",
+        animation_value_type="NonNegativeLength",
     )}
 % endfor

components/style/values/generics/box.rs

@@ -88,6 +88,8 @@ impl<L> ToAnimatedZero for VerticalAlign<L> {
     PartialEq,
     SpecifiedValueInfo,
     ToComputedValue,
+    ToAnimatedValue,
+    ToAnimatedZero,
     ToResolvedValue,
     ToShmem,
 )]