Add CSS system colors Mark and MarkText.

CSS Color Module Level 4 defines new system colors
(https://www.w3.org/TR/css-color-4/#css-system-colors).
This CL implements Mark and MarkText.

Bug: 1299441
Change-Id: Id184ee58c49e7d55a32b3776e5d0d9489eb4e9cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3536909
Reviewed-by: Stephen Chenney <[email protected]>
Commit-Queue: Stephen Chenney <[email protected]>
Cr-Commit-Position: refs/heads/main@{#983348}

css/css-color/parsing/system-color-valid.html

@@ -23,6 +23,8 @@
 test_valid_value("color", "Highlight", "highlight");
 test_valid_value("color", "HighlightText", "highlighttext");
 test_valid_value("color", "LinkText", "linktext");
+test_valid_value("color", "Mark", "mark");
+test_valid_value("color", "MarkText", "marktext");
 test_valid_value("color", "VisitedText", "visitedtext");
 test_valid_value("color", "SelectedItem", "selecteditem");
 test_valid_value("color", "SelectedItemText", "selecteditemtext");

css/css-color/system-color-consistency.html

@@ -19,12 +19,16 @@
   <div id="buttons">
     <button name="button"></button><input type="submit" name="submit button"><input type="reset" name="reset button">
   </div>
+  <mark id="mark">Marked text</mark>
   <script>
     for (let element of document.getElementById("buttons").children) {
       style = document.defaultView.getComputedStyle(element);
       test_computed_value(`color`, `ButtonText`, style.getPropertyValue('color'), 'has the same color as text on a ' + element.name);
     }
-    // Test with no specified target contrast
+    // Mark and MarkText
+    style = document.defaultView.getComputedStyle(document.getElementById('mark'));
+    test_computed_value('color', 'Mark', style.getPropertyValue('background-color'), 'has the same color as the background-color of a mark element');
+    test_computed_value('color', 'MarkText', style.getPropertyValue('color'), 'has the same color as the color of a mark element');
   </script>
 </body>