Add style_traits crate to improve crate separation,

closes #7353

components/style_traits/values.rs

@@ -0,0 +1,55 @@
+/* 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/. */
+
+#[macro_export]
+macro_rules! define_css_keyword_enum {
+    ($name: ident: $( $css: expr => $variant: ident ),+,) => {
+        define_css_keyword_enum!($name: $( $css => $variant ),+);
+    };
+    ($name: ident: $( $css: expr => $variant: ident ),+) => {
+        #[allow(non_camel_case_types)]
+        #[derive(Clone, Eq, PartialEq, Copy, Hash, RustcEncodable, Debug, HeapSizeOf)]
+        #[derive(Deserialize, Serialize)]
+        pub enum $name {
+            $( $variant ),+
+        }
+
+        impl $name {
+            pub fn parse(input: &mut ::cssparser::Parser) -> Result<$name, ()> {
+                match_ignore_ascii_case! { try!(input.expect_ident()),
+                                           $( $css => Ok($name::$variant) ),+
+                                           _ => Err(())
+                }
+            }
+        }
+
+        impl ::cssparser::ToCss for $name {
+            fn to_css<W>(&self, dest: &mut W) -> ::std::fmt::Result
+                where W: ::std::fmt::Write {
+                    match *self {
+                        $( $name::$variant => dest.write_str($css) ),+
+                    }
+                }
+        }
+    }
+}
+
+
+pub mod specified {
+    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+    pub enum AllowedNumericType {
+        All,
+        NonNegative
+    }
+
+    impl AllowedNumericType {
+        #[inline]
+        pub fn is_ok(&self, value: f32) -> bool {
+            match *self {
+                AllowedNumericType::All => true,
+                AllowedNumericType::NonNegative => value >= 0.,
+            }
+        }
+    }
+}