Auto merge of #18081 - hiikezoe:interpolation-with-auto, r=birtles,boris,mantaroh

Fix interpolation between auto and other values

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1387939

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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components/style/properties/gecko.mako.rs

@@ -5434,10 +5434,10 @@ clip-path
     ${impl_simple_copy('column_count', 'mColumnCount')}
 
     pub fn clone_column_count(&self) -> longhands::column_count::computed_value::T {
-        use gecko_bindings::structs::NS_STYLE_COLUMN_COUNT_AUTO;
+        use gecko_bindings::structs::{NS_STYLE_COLUMN_COUNT_AUTO, nsStyleColumn_kMaxColumnCount};
         if self.gecko.mColumnCount != NS_STYLE_COLUMN_COUNT_AUTO {
-            debug_assert!((self.gecko.mColumnCount as i32) >= 0 &&
-                          (self.gecko.mColumnCount as i32) < i32::max_value());
+            debug_assert!(self.gecko.mColumnCount >= 1 &&
+                          self.gecko.mColumnCount <= nsStyleColumn_kMaxColumnCount);
             Either::First((self.gecko.mColumnCount as i32).into())
         } else {
             Either::Second(Auto)

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

@@ -863,7 +863,7 @@ impl Animatable for f64 {
 impl Animatable for i32 {
     #[inline]
     fn add_weighted(&self, other: &i32, self_portion: f64, other_portion: f64) -> Result<Self, ()> {
-        Ok((*self as f64 * self_portion + *other as f64 * other_portion).round() as i32)
+        Ok((*self as f64 * self_portion + *other as f64 * other_portion + 0.5).floor() as i32)
     }
 }
 
@@ -2410,10 +2410,7 @@ impl<T, U> Animatable for Either<T, U>
             (Either::Second(ref this), Either::Second(ref other)) => {
                 this.add_weighted(&other, self_portion, other_portion).map(Either::Second)
             },
-            _ => {
-                let result = if self_portion > other_portion {*self} else {*other};
-                Ok(result)
-            }
+            _ => Err(()),
         }
     }
 }