Auto merge of #16963 - BorisChiou:stylo/animation/omta, r=emilio

stylo: Bug 1334036 - Enable animations running on compositor.

These are interdependent patches of Bug 1334036, which enables off-main thread animations. We add one FFI to get the property id set which overriding animations, so we can make sure the cascade result is correct for off-main thread animations.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1334036](https://bugzilla.mozilla.org/show_bug.cgi?id=1334036)
- [X] These changes do not require tests because we support off-main thread animation only on Gecko, and there are enough test cases there.

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components/style/properties/gecko.mako.rs

@@ -2241,7 +2241,7 @@ fn static_assert() {
             % endfor
         }
     </%def>
-    pub fn convert_transform(input: Vec<longhands::transform::computed_value::ComputedOperation>,
+    pub fn convert_transform(input: &[longhands::transform::computed_value::ComputedOperation],
                              output: &mut structs::root::RefPtr<structs::root::nsCSSValueSharedList>) {
         use gecko_bindings::structs::nsCSSKeyword::*;
         use gecko_bindings::sugar::refptr::RefPtr;
@@ -2261,7 +2261,7 @@ fn static_assert() {
             let servo = iter.next().expect("Gecko_NewCSSValueSharedList should create a shared \
                                             value list of the same length as the transform vector");
             unsafe {
-                match servo {
+                match *servo {
                     ${transform_function_arm("Matrix", "matrix3d", ["number"] * 16)}
                     ${transform_function_arm("MatrixWithPercents", "matrix3d", ["number"] * 12 + ["lop"] * 2
                                              + ["length"] + ["number"])}
@@ -2287,7 +2287,7 @@ fn static_assert() {
             }
             return;
         };
-        Self::convert_transform(vec, &mut self.gecko.mSpecifiedTransform);
+        Self::convert_transform(&vec, &mut self.gecko.mSpecifiedTransform);
     }
 
     pub fn copy_transform_from(&mut self, other: &Self) {

components/style/properties/properties.mako.rs

@@ -250,7 +250,7 @@ pub mod animated_properties {
 }
 
 /// A set of longhand properties
-#[derive(Clone)]
+#[derive(Clone, PartialEq)]
 pub struct LonghandIdSet {
     storage: [u32; (${len(data.longhands)} - 1 + 32) / 32]
 }
@@ -954,7 +954,7 @@ impl PropertyId {
         }
     }
 
-    /// Returns a property id from Gecko's nsCSSPropertyID.
+    /// Returns an nsCSSPropertyID.
     #[cfg(feature = "gecko")]
     #[allow(non_upper_case_globals)]
     pub fn to_nscsspropertyid(&self) -> Result<nsCSSPropertyID, ()> {