style: Use cbindgen for ExtremumLength.

ExtremumLength is the keyword type for css sizing properties, so we
could use cbindgen.

In Gecko, we use nsStyleCoord to store the sizing properties, and use
integer values to check the enum values, so I keep the macros in nsStyleConsts.
Even though we need to convert the enum type into integer, we still have
benefits to reduce the complexity of converting Rust into C++, and leave
the simplified mappings in C++ for better readability.

Differential Revision: https://phabricator.services.mozilla.com/D7535

components/style/cbindgen.toml

@@ -50,6 +50,7 @@ include = [
   "ComputedTimingFunction",
   "Display",
   "DisplayMode",
+  "ExtremumLength",
   "FillRule",
   "FontDisplay",
   "FontFaceSourceListComponent",

components/style/gecko/values.rs

@@ -362,40 +362,13 @@ impl GeckoStyleCoordConvertible for Normal {
 
 impl GeckoStyleCoordConvertible for ExtremumLength {
     fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
-        use crate::gecko_bindings::structs::{
-            NS_STYLE_WIDTH_AVAILABLE, NS_STYLE_WIDTH_FIT_CONTENT,
-        };
-        use crate::gecko_bindings::structs::{
-            NS_STYLE_WIDTH_MAX_CONTENT, NS_STYLE_WIDTH_MIN_CONTENT,
-        };
-        coord.set_value(CoordDataValue::Enumerated(match *self {
-            ExtremumLength::MozMaxContent => NS_STYLE_WIDTH_MAX_CONTENT,
-            ExtremumLength::MozMinContent => NS_STYLE_WIDTH_MIN_CONTENT,
-            ExtremumLength::MozFitContent => NS_STYLE_WIDTH_FIT_CONTENT,
-            ExtremumLength::MozAvailable => NS_STYLE_WIDTH_AVAILABLE,
-        }))
+        coord.set_value(CoordDataValue::Enumerated(*self as u32));
     }
 
     fn from_gecko_style_coord<T: CoordData>(coord: &T) -> Option<Self> {
-        use crate::gecko_bindings::structs::{
-            NS_STYLE_WIDTH_AVAILABLE, NS_STYLE_WIDTH_FIT_CONTENT,
-        };
-        use crate::gecko_bindings::structs::{
-            NS_STYLE_WIDTH_MAX_CONTENT, NS_STYLE_WIDTH_MIN_CONTENT,
-        };
+        use num_traits::FromPrimitive;
         match coord.as_value() {
-            CoordDataValue::Enumerated(NS_STYLE_WIDTH_MAX_CONTENT) => {
-                Some(ExtremumLength::MozMaxContent)
-            },
-            CoordDataValue::Enumerated(NS_STYLE_WIDTH_MIN_CONTENT) => {
-                Some(ExtremumLength::MozMinContent)
-            },
-            CoordDataValue::Enumerated(NS_STYLE_WIDTH_FIT_CONTENT) => {
-                Some(ExtremumLength::MozFitContent)
-            },
-            CoordDataValue::Enumerated(NS_STYLE_WIDTH_AVAILABLE) => {
-                Some(ExtremumLength::MozAvailable)
-            },
+            CoordDataValue::Enumerated(v) => ExtremumLength::from_u32(v),
             _ => None,
         }
     }

components/style/values/computed/length.rs

@@ -975,13 +975,15 @@ pub type NonNegativeLengthOrPercentageOrNormal = Either<NonNegativeLengthOrPerce
     Copy,
     Debug,
     Eq,
+    FromPrimitive,
     MallocSizeOf,
     Parse,
     PartialEq,
     SpecifiedValueInfo,
     ToComputedValue,
     ToCss,
 )]
+#[repr(u8)]
 pub enum ExtremumLength {
     MozMaxContent,
     MozMinContent,