style: Add a ValueInfo trait for exposing types needed by devtools.

Most of types just derive it using proc_macro directly. Some of value
types need manual impl.

In my current plan, this new trait will be used in bug 1434130 to expose
values as well.

Bug: 1455576
Reviewed-by: emilio
MozReview-Commit-ID: LI7fy45VkRw

components/style/values/generics/url.rs

@@ -9,8 +9,9 @@ use parser::{Parse, ParserContext};
 use style_traits::ParseError;
 
 /// An image url or none, used for example in list-style-image
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToComputedValue,
+         ToCss)]
 pub enum UrlOrNone<Url> {
     /// `none`
     None,