style: Add CAN_ANIMATE_ON_COMPOSITOR in Servo side and propagate it to ServoCSSPropList.h.

Bug: 1454830
Reviewed-by: emilio
MozReview-Commit-ID: 2OBCliDY02g

components/style/properties/longhand/box.mako.rs

@@ -410,7 +410,8 @@ ${helpers.predefined_type(
     extra_prefixes=transform_extra_prefixes,
     animation_value_type="ComputedValue",
     gecko_ffi_name="mSpecifiedTransform",
-    flags="CREATES_STACKING_CONTEXT FIXPOS_CB GETCS_NEEDS_LAYOUT_FLUSH",
+    flags="CREATES_STACKING_CONTEXT FIXPOS_CB \
+           GETCS_NEEDS_LAYOUT_FLUSH CAN_ANIMATE_ON_COMPOSITOR",
     spec="https://drafts.csswg.org/css-transforms/#propdef-transform",
     servo_restyle_damage="reflow_out_of_flow"
 )}

components/style/properties/longhand/effects.mako.rs

@@ -7,13 +7,16 @@
 // Box-shadow, etc.
 <% data.new_style_struct("Effects", inherited=False) %>
 
-${helpers.predefined_type("opacity",
-                          "Opacity",
-                          "1.0",
-                          animation_value_type="ComputedValue",
-                          flags="CREATES_STACKING_CONTEXT APPLIES_TO_PLACEHOLDER",
-                          spec="https://drafts.csswg.org/css-color/#opacity",
-                          servo_restyle_damage = "reflow_out_of_flow")}
+${helpers.predefined_type(
+    "opacity",
+    "Opacity",
+    "1.0",
+    animation_value_type="ComputedValue",
+    flags="CREATES_STACKING_CONTEXT APPLIES_TO_PLACEHOLDER \
+           CAN_ANIMATE_ON_COMPOSITOR",
+    spec="https://drafts.csswg.org/css-color/#opacity",
+    servo_restyle_damage = "reflow_out_of_flow"
+)}
 
 ${helpers.predefined_type(
     "box-shadow",

components/style/properties/properties.mako.rs

@@ -788,6 +788,8 @@ bitflags! {
         /// This property's getComputedStyle implementation requires layout
         /// to be flushed.
         const GETCS_NEEDS_LAYOUT_FLUSH = 0;
+        /// This property can be animated on the compositor.
+        const CAN_ANIMATE_ON_COMPOSITOR = 0;
     }
 }