use deserialize_from for faster deserialization

This soft-forks serde_derive to add a deserialize_from derivation for
repr(u8) enums.

Cargo.toml

@@ -8,3 +8,7 @@ members = [
 [profile.release]
 debug = true
 panic = "abort"
+
+[replace]
+"serde:1.0.23" = { git = "https://github.com/gankro/serde", branch = "deserialize_from_enums3" }
+"serde_derive:1.0.23" = { git = "https://github.com/gankro/serde", branch = "deserialize_from_enums3", feature="deserialize_from" }

webrender_api/Cargo.toml

@@ -17,7 +17,7 @@ byteorder = "1.2.1"
 euclid = "0.15"
 ipc-channel = {version = "0.9", optional = true}
 serde = { version = "1.0.23", features = ["rc", "derive"] }
-serde_derive = { version = "1.0.23" }
+serde_derive = { version = "1.0.23", features = ["deserialize_from"] }
 time = "0.1"
 
 [target.'cfg(target_os = "macos")'.dependencies]

webrender_api/src/display_item.rs

@@ -88,6 +88,7 @@ impl LayerPrimitiveInfo {
 pub type LayoutPrimitiveInfo = PrimitiveInfo<LayoutPixel>;
 pub type LayerPrimitiveInfo = PrimitiveInfo<LayerPixel>;
 
+#[repr(u8)]
 #[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]
 pub enum SpecificDisplayItem {
     Clip(ClipDisplayItem),

webrender_api/src/display_list.rs

@@ -225,8 +225,12 @@ impl<'a> BuiltDisplayListIter<'a> {
                 return None;
             }
 
-            self.cur_item = bincode::deserialize_from(&mut UnsafeReader::new(&mut self.data), bincode::Infinite)
-                .expect("MEH: malicious process?");
+            {
+                let reader = bincode::read_types::IoReader::new(UnsafeReader::new(&mut self.data));
+                let mut deserializer = bincode::Deserializer::new(reader, bincode::Infinite);
+                self.cur_item.deserialize_from(&mut deserializer)
+                    .expect("MEH: malicious process?");
+            }
 
             match self.cur_item.item {
                 SetGradientStops => {