Introduce ComputedUrl

Add web platform tests for computed URL styles

Mark url with no original or resolved unreachable

Update the WPT manifest for new url tests

components/style/values/computed/mod.rs

@@ -12,10 +12,14 @@ use media_queries::Device;
 #[cfg(feature = "gecko")]
 use properties;
 use properties::{ComputedValues, StyleBuilder};
+#[cfg(feature = "servo")]
+use servo_url::ServoUrl;
 use std::f32;
 use std::f64;
 use std::f64::consts::PI;
 use std::fmt;
+#[cfg(feature = "servo")]
+use std::sync::Arc;
 use style_traits::ToCss;
 use super::{CSSFloat, CSSInteger};
 use super::generics::{GreaterThanOrEqualToOne, NonNegative};
@@ -39,9 +43,8 @@ pub use self::image::{Gradient, GradientItem, Image, ImageLayer, LineDirection,
 pub use self::gecko::ScrollSnapPoint;
 pub use self::rect::LengthOrNumberRect;
 pub use super::{Auto, Either, None_};
-pub use super::specified::{BorderStyle, UrlOrNone};
+pub use super::specified::BorderStyle;
 pub use super::generics::grid::GridLine;
-pub use super::specified::url::SpecifiedUrl;
 pub use self::length::{CalcLengthOrPercentage, Length, LengthOrNone, LengthOrNumber, LengthOrPercentage};
 pub use self::length::{LengthOrPercentageOrAuto, LengthOrPercentageOrNone, MaxLength, MozLength};
 pub use self::length::NonNegativeLengthOrPercentage;
@@ -684,3 +687,45 @@ impl ToComputedValue for specified::Percentage {
         specified::Percentage::new(computed.0)
     }
 }
+
+/// The computed value of a CSS `url()`, resolved relative to the stylesheet URL.
+#[cfg(feature = "servo")]
+#[derive(Clone, Debug, HeapSizeOf, Serialize, Deserialize, PartialEq)]
+pub enum ComputedUrl {
+    /// The `url()` was invalid or it wasn't specified by the user.
+    Invalid(Arc<String>),
+    /// The resolved `url()` relative to the stylesheet URL.
+    Valid(ServoUrl),
+}
+
+/// TODO: Properly build ComputedUrl for gecko
+#[cfg(feature = "gecko")]
+pub type ComputedUrl = specified::url::SpecifiedUrl;
+
+#[cfg(feature = "servo")]
+impl ComputedUrl {
+    /// Returns the resolved url if it was valid.
+    pub fn url(&self) -> Option<&ServoUrl> {
+        match *self {
+            ComputedUrl::Valid(ref url) => Some(url),
+            _ => None,
+        }
+    }
+}
+
+#[cfg(feature = "servo")]
+impl ToCss for ComputedUrl {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        let string = match *self {
+            ComputedUrl::Valid(ref url) => url.as_str(),
+            ComputedUrl::Invalid(ref invalid_string) => invalid_string,
+        };
+
+        dest.write_str("url(")?;
+        string.to_css(dest)?;
+        dest.write_str(")")
+    }
+}
+
+/// <url> | <none>
+pub type UrlOrNone = Either<ComputedUrl, None_>;