style: Move Ratio into independent files.

Based on https://drafts.csswg.org/css-values/#ratios, <ratio> should be
a general types in css values, and now the media query and the position use
this type, so let's move it into the independent files.

Differential Revision: https://phabricator.services.mozilla.com/D106218

components/style/values/specified/ratio.rs

@@ -0,0 +1,32 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! Specified types for <ratio>.
+//!
+//! [ratio]: https://drafts.csswg.org/css-values/#ratios
+
+use crate::parser::{Parse, ParserContext};
+use crate::values::generics::ratio::Ratio as GenericRatio;
+use crate::values::specified::NonNegativeNumber;
+use crate::One;
+use cssparser::Parser;
+use style_traits::ParseError;
+
+/// A specified <ratio> value.
+pub type Ratio = GenericRatio<NonNegativeNumber>;
+
+impl Parse for Ratio {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let a = NonNegativeNumber::parse(context, input)?;
+        let b = match input.try_parse(|input| input.expect_delim('/')) {
+            Ok(()) => NonNegativeNumber::parse(context, input)?,
+            _ => One::one(),
+        };
+
+        Ok(GenericRatio(a, b))
+    }
+}