Use generics for background-size property

components/style/values/specified/background.rs

@@ -0,0 +1,29 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Specified types for CSS values related to backgrounds.
+
+use cssparser::Parser;
+use parser::{Parse, ParserContext};
+use values::generics::background::BackgroundSize as GenericBackgroundSize;
+use values::specified::length::LengthOrPercentageOrAuto;
+
+/// A specified value for the `background-size` property.
+pub type BackgroundSize = GenericBackgroundSize<LengthOrPercentageOrAuto>;
+
+impl Parse for BackgroundSize {
+    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
+        if let Ok(width) = input.try(|i| LengthOrPercentageOrAuto::parse_non_negative(context, i)) {
+            let height = input
+                .try(|i| LengthOrPercentageOrAuto::parse_non_negative(context, i))
+                .unwrap_or(LengthOrPercentageOrAuto::Auto);
+            return Ok(GenericBackgroundSize::Explicit { width: width, height: height });
+        }
+        match_ignore_ascii_case! { &input.expect_ident()?,
+            "cover" => Ok(GenericBackgroundSize::Cover),
+            "contain" => Ok(GenericBackgroundSize::Contain),
+            _ => Err(()),
+        }
+    }
+}