Bug 1374233 - Part 7: Add NonNegativeLengthOrPercentage.

For padding-{*} and grid-{*}-gap.

MozReview-Commit-ID: 81G0b1k6JnD

components/style/values/computed/length.rs

@@ -12,6 +12,7 @@ use style_traits::values::specified::AllowedLengthType;
 use super::{Number, ToComputedValue, Context};
 use values::{Auto, CSSFloat, Either, ExtremumLength, None_, Normal, specified};
 use values::computed::{NonNegativeAu, NonNegativeNumber};
+use values::generics::NonNegative;
 use values::specified::length::{AbsoluteLength, FontBaseSize, FontRelativeLength};
 use values::specified::length::ViewportPercentageLength;
 
@@ -551,6 +552,36 @@ impl ToComputedValue for specified::LengthOrPercentageOrNone {
     }
 }
 
+/// A wrapper of LengthOrPercentage, whose value must be >= 0.
+pub type NonNegativeLengthOrPercentage = NonNegative<LengthOrPercentage>;
+
+impl From<LengthOrPercentage> for NonNegativeLengthOrPercentage {
+    #[inline]
+    fn from(lop: LengthOrPercentage) -> Self {
+        NonNegative::<LengthOrPercentage>(lop)
+    }
+}
+
+impl NonNegativeLengthOrPercentage {
+    /// Get zero value.
+    #[inline]
+    pub fn zero() -> Self {
+        NonNegative::<LengthOrPercentage>(LengthOrPercentage::zero())
+    }
+
+    /// Returns true if the computed value is absolute 0 or 0%.
+    #[inline]
+    pub fn is_definitely_zero(&self) -> bool {
+        self.0.is_definitely_zero()
+    }
+
+    /// Returns the used value.
+    #[inline]
+    pub fn to_used_value(&self, containing_length: Au) -> Au {
+        self.0.to_used_value(containing_length)
+    }
+}
+
 /// A computed `<length>` value.
 pub type Length = Au;