Auto merge of #16166 - streichgeorg:initial-letter, r=emilio

initial-letter property

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Implemented parsing and serialization for the initial-letter property.

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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 #15959 (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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tests/unit/style/parsing/mod.rs

@@ -99,6 +99,7 @@ mod outline;
 mod position;
 mod selectors;
 mod supports;
+mod text;
 mod text_overflow;
 mod transition_timing_function;
 mod ui;

tests/unit/style/parsing/text.rs

@@ -0,0 +1,26 @@
+/* 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 initial_letter_should_be_parsed_correctly() {
+    use style::properties::longhands::initial_letter;
+
+    assert_roundtrip_with_context!(initial_letter::parse, "1.5");
+    assert_roundtrip_with_context!(initial_letter::parse, "1.5 3");
+    assert_roundtrip_with_context!(initial_letter::parse, "normal");
+}
+
+#[test]
+fn initial_letter_doesnt_parse_invalid_input() {
+    use style::properties::longhands::initial_letter;
+
+    assert!(parse(initial_letter::parse, "1.5x 5").is_err());
+}