style: Use Rust types for some misc properties.

-moz-tab-size, border-image-outset and border-image-slice.

This is not a particularly interesting patch, just removes some code. We can
remove way more code when a few related properties are also ported.

Differential Revision: https://phabricator.services.mozilla.com/D19825

components/style/values/specified/rect.rs

@@ -4,22 +4,8 @@
 
 //! Specified types for CSS borders.
 
-use crate::parser::ParserContext;
 use crate::values::generics::rect::Rect;
-use crate::values::specified::length::LengthOrNumber;
-use cssparser::Parser;
-use style_traits::ParseError;
+use crate::values::specified::length::NonNegativeLengthOrNumber;
 
 /// A specified rectangle made of four `<length-or-number>` values.
-pub type LengthOrNumberRect = Rect<LengthOrNumber>;
-
-impl LengthOrNumberRect {
-    /// Parses a `LengthOrNumberRect`, rejecting negative values.
-    #[inline]
-    pub fn parse_non_negative<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Rect::parse_with(context, input, LengthOrNumber::parse_non_negative)
-    }
-}
+pub type NonNegativeLengthOrNumberRect = Rect<NonNegativeLengthOrNumber>;