Implement parsing/serialization of will-change

tests/unit/style/parsing/box_.rs

@@ -0,0 +1,28 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use cssparser::Parser;
+use media_queries::CSSErrorReporterTest;
+use parsing::parse;
+use style::parser::ParserContext;
+use style::stylesheets::Origin;
+use style_traits::ToCss;
+
+#[test]
+fn test_will_change() {
+    use style::properties::longhands::will_change;
+
+    assert_roundtrip_with_context!(will_change::parse, "auto");
+    assert_roundtrip_with_context!(will_change::parse, "scroll-position");
+    assert_roundtrip_with_context!(will_change::parse, "contents");
+    assert_roundtrip_with_context!(will_change::parse, "transition");
+    assert_roundtrip_with_context!(will_change::parse, "opacity, transform");
+
+    assert!(parse(will_change::parse, "will-change").is_err());
+    assert!(parse(will_change::parse, "all").is_err());
+    assert!(parse(will_change::parse, "none").is_err());
+    assert!(parse(will_change::parse, "contents, auto").is_err());
+    assert!(parse(will_change::parse, "contents, inherit, initial").is_err());
+    assert!(parse(will_change::parse, "transform scroll-position").is_err());
+}

tests/unit/style/parsing/mod.rs

@@ -85,6 +85,7 @@ mod animation;
 mod background;
 mod basic_shape;
 mod border;
+mod box_;
 mod column;
 mod effects;
 mod font;