Make use of predefined_type for some aliased types

components/style/values/computed/mod.rs

@@ -4,7 +4,6 @@
 
 //! Computed values.
 
-use app_units::Au;
 use euclid::size::Size2D;
 use font_metrics::FontMetricsProvider;
 use media_queries::Device;
@@ -16,6 +15,7 @@ use super::generics::BorderRadiusSize as GenericBorderRadiusSize;
 use super::specified;
 use super::specified::grid::{TrackBreadth as GenericTrackBreadth, TrackSize as GenericTrackSize};
 
+pub use app_units::Au;
 pub use cssparser::Color as CSSColor;
 pub use self::image::{AngleOrCorner, EndingShape as GradientShape, Gradient, GradientKind, Image, ImageRect};
 pub use self::image::{LengthOrKeyword, LengthOrPercentageOrKeyword};

components/style/values/computed/position.rs

@@ -59,7 +59,23 @@ pub type HorizontalPosition = GenericHorizontalPosition<LengthOrPercentage>;
 
 impl Copy for HorizontalPosition {}
 
+impl HorizontalPosition {
+    #[inline]
+    /// Create a zero position value.
+    pub fn zero() -> HorizontalPosition {
+        GenericHorizontalPosition(LengthOrPercentage::Percentage(0.0))
+    }
+}
+
 /// The computed value of a vertical `<position>`
 pub type VerticalPosition = GenericVerticalPosition<LengthOrPercentage>;
 
 impl Copy for VerticalPosition {}
+
+impl VerticalPosition {
+    #[inline]
+    /// Create a zero position value.
+    pub fn zero() -> VerticalPosition {
+        GenericVerticalPosition(LengthOrPercentage::Percentage(0.0))
+    }
+}

components/style/values/specified/position.rs

@@ -219,6 +219,18 @@ impl ToComputedValue for HorizontalPosition {
     }
 }
 
+impl HorizontalPosition {
+    #[inline]
+    /// Initial specified value for vertical position (`top` keyword).
+    pub fn left() -> HorizontalPosition {
+        GenericHorizontalPosition(PositionValue {
+            keyword: Some(Keyword::Left),
+            position: None,
+        })
+    }
+}
+
+
 /// The specified value of vertical `<position>`
 pub type VerticalPosition = GenericVerticalPosition<PositionValue<LengthOrPercentage>>;
 
@@ -238,3 +250,14 @@ impl ToComputedValue for VerticalPosition {
         })
     }
 }
+
+impl VerticalPosition {
+    #[inline]
+    /// Initial specified value for vertical position (`top` keyword).
+    pub fn top() -> VerticalPosition {
+        GenericVerticalPosition(PositionValue {
+            keyword: Some(Keyword::Top),
+            position: None,
+        })
+    }
+}