Bug 1374233 - Part 11: Implement ToAnimatedValue for background-size.

MozReview-Commit-ID: DMcvpaqHdy9

components/style/values/computed/background.rs

@@ -5,7 +5,8 @@
 //! Computed types for CSS values related to backgrounds.
 
 use properties::animated_properties::{Animatable, RepeatableListAnimatable};
-use values::animated::ToAnimatedZero;
+use properties::longhands::background_size::computed_value::T as BackgroundSizeList;
+use values::animated::{ToAnimatedValue, ToAnimatedZero};
 use values::computed::length::LengthOrPercentageOrAuto;
 use values::generics::background::BackgroundSize as GenericBackgroundSize;
 
@@ -56,3 +57,52 @@ impl ToAnimatedZero for BackgroundSize {
     #[inline]
     fn to_animated_zero(&self) -> Result<Self, ()> { Err(()) }
 }
+
+impl ToAnimatedValue for BackgroundSize {
+    type AnimatedValue = Self;
+
+    #[inline]
+    fn to_animated_value(self) -> Self {
+        self
+    }
+
+    #[inline]
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+        use app_units::Au;
+        use values::computed::Percentage;
+        let clamp_animated_value = |value: LengthOrPercentageOrAuto| -> LengthOrPercentageOrAuto {
+            match value {
+                LengthOrPercentageOrAuto::Length(len) => {
+                    LengthOrPercentageOrAuto::Length(Au(::std::cmp::max(len.0, 0)))
+                },
+                LengthOrPercentageOrAuto::Percentage(percent) => {
+                    LengthOrPercentageOrAuto::Percentage(Percentage(percent.0.max(0.)))
+                },
+                _ => value
+            }
+        };
+        match animated {
+            GenericBackgroundSize::Explicit { width, height } => {
+                GenericBackgroundSize::Explicit {
+                    width: clamp_animated_value(width),
+                    height: clamp_animated_value(height)
+                }
+            },
+            _ => animated
+        }
+    }
+}
+
+impl ToAnimatedValue for BackgroundSizeList {
+    type AnimatedValue = Self;
+
+    #[inline]
+    fn to_animated_value(self) -> Self {
+        self
+    }
+
+    #[inline]
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+        BackgroundSizeList(ToAnimatedValue::from_animated_value(animated.0))
+    }
+}