Auto merge of #16568 - WholeGrainGoats:master, r=Manishearth

font-feature-settings gecko glue code

<!-- Please describe your changes on the following line: -->
FeatureTagValue value property changed to use u32. ToCss for
FeatureTagValue changed to allow conversion from u32 to string. Parse
for the same struct updated to convert from string to u32. Added two
functions to transfer settings to gecko and copy settings.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #15975  (github issue number if applicable).

<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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tests/unit/style/Cargo.toml

@@ -13,6 +13,7 @@ doctest = false
 testing = ["style/testing"]
 
 [dependencies]
+byteorder = "1.0"
 app_units = "0.4"
 cssparser = "0.13"
 euclid = "0.11"

tests/unit/style/lib.rs

@@ -6,6 +6,7 @@
 #![feature(plugin, test)]
 
 extern crate app_units;
+extern crate byteorder;
 extern crate cssparser;
 extern crate euclid;
 #[macro_use] extern crate html5ever;

tests/unit/style/parsing/font.rs

@@ -10,38 +10,47 @@ use style_traits::ToCss;
 
 #[test]
 fn font_feature_settings_should_parse_properly() {
+    use byteorder::{ReadBytesExt, NativeEndian};
+    use std::io::Cursor;
+
     let normal = parse_longhand!(font_feature_settings, "normal");
     let normal_computed = computed_value::T::Normal;
     assert_eq!(normal, normal_computed);
 
+    let mut a_d_bytes = Cursor::new(b"abcd");
+    let mut e_h_bytes = Cursor::new(b"efgh");
+
+    let abcd = a_d_bytes.read_u32::<NativeEndian>().unwrap();
+    let efgh = e_h_bytes.read_u32::<NativeEndian>().unwrap();
+
     let on = parse_longhand!(font_feature_settings, "\"abcd\" on");
     let on_computed = computed_value::T::Tag(vec![
-        FeatureTagValue { tag: String::from("abcd"), value: 1 }
+        FeatureTagValue { tag: abcd, value: 1 }
     ]);
     assert_eq!(on, on_computed);
 
     let off = parse_longhand!(font_feature_settings, "\"abcd\" off");
     let off_computed = computed_value::T::Tag(vec![
-        FeatureTagValue { tag: String::from("abcd"), value: 0 }
+        FeatureTagValue { tag: abcd, value: 0 }
     ]);
     assert_eq!(off, off_computed);
 
     let no_value = parse_longhand!(font_feature_settings, "\"abcd\"");
     let no_value_computed = computed_value::T::Tag(vec![
-        FeatureTagValue { tag: String::from("abcd"), value: 1 }
+        FeatureTagValue { tag: abcd, value: 1 }
     ]);
     assert_eq!(no_value, no_value_computed);
 
     let pos_integer = parse_longhand!(font_feature_settings, "\"abcd\" 100");
     let pos_integer_computed = computed_value::T::Tag(vec![
-        FeatureTagValue { tag: String::from("abcd"), value: 100 }
+        FeatureTagValue { tag: abcd, value: 100 }
     ]);
     assert_eq!(pos_integer, pos_integer_computed);
 
     let multiple = parse_longhand!(font_feature_settings, "\"abcd\" off, \"efgh\"");
     let multiple_computed = computed_value::T::Tag(vec![
-        FeatureTagValue { tag: String::from("abcd"), value: 0 },
-        FeatureTagValue { tag: String::from("efgh"), value: 1 }
+        FeatureTagValue { tag: abcd, value: 0 },
+        FeatureTagValue { tag: efgh, value: 1 }
     ]);
     assert_eq!(multiple, multiple_computed);
 }