Support clamp() in CSSNumericValue.parse()

This patch supports parsing 'clamp(MIN, VAL, MAX)' into a
CSSNumericValue via the parse() method.

This was missed in the previous implementation of clamp(), and should be
the last missing piece of the implementation.

Bug: 825895
Change-Id: I6da8113d62b1416dc6d3521b58134932b257ca62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1832147
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701536}

third_party/blink/renderer/core/css/cssom/css_numeric_value.cc

@@ -253,8 +253,8 @@ CSSNumericValue* CSSNumericValue::parse(const String& css_text,
           range.Peek().FunctionId() == CSSValueID::kWebkitCalc ||
           (RuntimeEnabledFeatures::CSSComparisonFunctionsEnabled() &&
            (range.Peek().FunctionId() == CSSValueID::kMin ||
-            range.Peek().FunctionId() == CSSValueID::kMax))) {
-        // TODO(crbug.com/825895): Support clamp() after min()/max() are done.
+            range.Peek().FunctionId() == CSSValueID::kMax ||
+            range.Peek().FunctionId() == CSSValueID::kClamp))) {
         CSSMathExpressionNode* expression =
             CSSMathExpressionNode::ParseCalc(range);
         if (expression)

third_party/blink/web_tests/external/wpt/css/css-typed-om/stylevalue-subclasses/numeric-objects/parse.tentative.html

@@ -37,4 +37,9 @@ test(() => {
   assert_style_value_equals(expected, CSSNumericValue.parse('max(10px, 10%)'));
 }, 'Parsing max() is successful');
 
+test(() => {
+  const expected = new CSSMathMax(CSS.px(10), new CSSMathMin(CSS.percent(10), CSS.px(20)));
+  assert_style_value_equals(expected, CSSNumericValue.parse('clamp(10px, 10%, 20px)'));
+}, 'Parsing clamp() is successful');
+
 </script>