style: Use serde to serialize LengthPercentage and StyleRayFunction.

We need to pass these two types into the compositor, so we need a better
way to serialize these rust types. We use serde and bincode to
serialize/deserialize them, and use ByteBuf to pass the &[u8] data
through IPC. We define StyleVecU8 for FFI usage only.

Differential Revision: https://phabricator.services.mozilla.com/D50688

components/style/values/computed/angle.rs

@@ -13,16 +13,17 @@ use std::{f32, f64};
 use style_traits::{CssWriter, ToCss};
 
 /// A computed angle in degrees.
-#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 #[derive(
     Add,
     Animate,
     Clone,
     Copy,
     Debug,
+    Deserialize,
     MallocSizeOf,
     PartialEq,
     PartialOrd,
+    Serialize,
     ToAnimatedZero,
     ToResolvedValue,
 )]