stylo: Implement scroll-snap-destination

MozReview-Commit-ID: 6mr4ktfeEGT

components/style/properties/gecko.mako.rs

@@ -1169,7 +1169,7 @@ fn static_assert() {
                           animation-iteration-count animation-timing-function
                           -moz-binding page-break-before page-break-after
                           scroll-snap-points-x scroll-snap-points-y transform
-                          scroll-snap-type-y perspective-origin transform-origin""" %>
+                          scroll-snap-type-y scroll-snap-destination perspective-origin transform-origin""" %>
 <%self:impl_trait style_struct_name="Box" skip_longhands="${skip_box_longhands}">
 
     // We manually-implement the |display| property until we get general
@@ -1340,6 +1340,13 @@ fn static_assert() {
 
     ${impl_coord_copy('scroll_snap_points_y', 'mScrollSnapPointsY')}
 
+    pub fn set_scroll_snap_destination(&mut self, v: longhands::scroll_snap_destination::computed_value::T) {
+        self.gecko.mScrollSnapDestination.mXPosition = v.horizontal.into();
+        self.gecko.mScrollSnapDestination.mYPosition = v.vertical.into();
+    }
+
+    ${impl_simple_copy('scroll_snap_destination', 'mScrollSnapDestination')}
+
     <%def name="transform_function_arm(name, keyword, items)">
         <%
             pattern = None

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

@@ -1049,6 +1049,12 @@ ${helpers.single_keyword("animation-fill-mode",
 </%helpers:longhand>
 
 
+${helpers.predefined_type("scroll-snap-destination",
+                          "Position",
+                          "computed::Position::zero()",
+                          products="gecko",
+                          spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-destination)",
+                          animatable=False)}
 
 <%helpers:longhand name="transform" products="gecko servo" extra_prefixes="webkit"
                    animatable="True"

components/style/values/computed/mod.rs

@@ -20,6 +20,7 @@ pub use super::specified::{Angle, BorderStyle, GridLine, Time, UrlOrNone};
 pub use super::specified::url::UrlExtraData;
 pub use self::length::{CalcLengthOrPercentage, Length, LengthOrNumber, LengthOrPercentage, LengthOrPercentageOrAuto};
 pub use self::length::{LengthOrPercentageOrAutoOrContent, LengthOrPercentageOrNone, LengthOrNone};
+pub use self::position::Position;
 
 pub mod basic_shape;
 pub mod image;

components/style/values/computed/position.rs

@@ -19,6 +19,16 @@ pub struct Position {
     pub vertical: LengthOrPercentage,
 }
 
+impl Position {
+    /// Construct a position at (0, 0)
+    pub fn zero() -> Self {
+        Position {
+            horizontal: LengthOrPercentage::zero(),
+            vertical: LengthOrPercentage::zero(),
+        }
+    }
+}
+
 impl ToCss for Position {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
         try!(self.horizontal.to_css(dest));

components/style/values/specified/mod.rs

@@ -27,6 +27,7 @@ pub use self::image::{SizeKeyword, VerticalDirection};
 pub use self::length::{FontRelativeLength, ViewportPercentageLength, CharacterWidth, Length, CalcLengthOrPercentage};
 pub use self::length::{Percentage, LengthOrNone, LengthOrNumber, LengthOrPercentage, LengthOrPercentageOrAuto};
 pub use self::length::{LengthOrPercentageOrNone, LengthOrPercentageOrAutoOrContent, NoCalcLength, CalcUnit};
+pub use self::position::{HorizontalPosition, Position, VerticalPosition};
 
 pub mod basic_shape;
 pub mod grid;