Auto merge of #16494 - mantaroh:animate_column, r=hiro

Make column-count/column-gap/column-width animatable.

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This is a PR for https://bugzilla.mozilla.org/show_bug.cgi?id=1355732.

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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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- [X] There are tests for these changes, a test case will be landed in web-platform-tests in https://bugzilla.mozilla.org/show_bug.cgi?id=1355732

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components/style/properties/gecko.mako.rs

@@ -679,6 +679,7 @@ impl Debug for ${style_struct.gecko_struct_name} {
         "LengthOrPercentageOrAuto": impl_style_coord,
         "LengthOrPercentageOrNone": impl_style_coord,
         "LengthOrNone": impl_style_coord,
+        "LengthOrNormal": impl_style_coord,
         "MaxLength": impl_style_coord,
         "MinLength": impl_style_coord,
         "Number": impl_simple,
@@ -3610,6 +3611,17 @@ 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;
+        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());
+            Either::First(self.gecko.mColumnCount as i32)
+        } else {
+            Either::Second(Auto)
+        }
+    }
+
     <% impl_app_units("column_rule_width", "mColumnRuleWidth", need_clone=True,
                       round_to_pixels=True) %>
 </%self:impl_trait>

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

@@ -29,7 +29,7 @@ use std::fmt;
 use style_traits::ToCss;
 use super::ComputedValues;
 use values::CSSFloat;
-use values::{Auto, Either};
+use values::{Auto, Either, Normal};
 use values::computed::{Angle, LengthOrPercentageOrAuto, LengthOrPercentageOrNone};
 use values::computed::{BorderRadiusSize, ClipRect, LengthOrNone};
 use values::computed::{CalcLengthOrPercentage, Context, LengthOrPercentage};
@@ -515,6 +515,13 @@ impl Interpolate for Auto {
     }
 }
 
+impl Interpolate for Normal {
+    #[inline]
+    fn interpolate(&self, _other: &Self, _progress: f64) -> Result<Self, ()> {
+        Ok(Normal)
+    }
+}
+
 impl <T> Interpolate for Option<T>
     where T: Interpolate,
 {

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

@@ -6,20 +6,19 @@
 
 <% data.new_style_struct("Column", inherited=False) %>
 
-// FIXME: This prop should be animatable.
 ${helpers.predefined_type("column-width",
                           "length::LengthOrAuto",
                           "Either::Second(Auto)",
                           initial_specified_value="Either::Second(Auto)",
                           parse_method="parse_non_negative_length",
                           extra_prefixes="moz",
-                          animation_type="none",
+                          animation_type="normal",
                           experimental=True,
                           spec="https://drafts.csswg.org/css-multicol/#propdef-column-width")}
 
 
-// FIXME: This prop should be animatable.
+${helpers.predefined_type("column-count",
-${helpers.predefined_type("column-count", "IntegerOrAuto",
+                          "IntegerOrAuto",
                           "Either::Second(Auto)",
                           parse_method="parse_positive",
                           initial_specified_value="Either::Second(Auto)",
@@ -28,14 +27,13 @@ ${helpers.predefined_type("column-count", "IntegerOrAuto",
                           extra_prefixes="moz",
                           spec="https://drafts.csswg.org/css-multicol/#propdef-column-count")}
 
-// FIXME: This prop should be animatable.
 ${helpers.predefined_type("column-gap",
                           "length::LengthOrNormal",
                           "Either::Second(Normal)",
                           parse_method='parse_non_negative_length',
                           extra_prefixes="moz",
                           experimental=True,
-                          animation_type="none",
+                          animation_type="normal",
                           spec="https://drafts.csswg.org/css-multicol/#propdef-column-gap")}
 
 ${helpers.single_keyword("column-fill", "balance auto", extra_prefixes="moz",