Do not simplify calculation across math functions

The existing code is too aggressive in simplifying calc() expressions
that, math functions (min/max etc) can be simplified away when they
can be directly resolved. This doesn't match the spec (*), and is fixed
in this patch.

(*) https://drafts.csswg.org/css-values-4/#math-function-simplify-a-calculation

Bug: 825895
Change-Id: Id5796299da50e40b09bc38bf0271c8f5cd7897de
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1825325Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700132}

third_party/blink/renderer/core/css/css_math_expression_node.cc

@@ -385,6 +385,9 @@ CSSMathExpressionNode* CSSMathExpressionBinaryOperation::CreateSimplified(
     const CSSMathExpressionNode* left_side,
     const CSSMathExpressionNode* right_side,
     CSSMathOperator op) {
+  if (left_side->IsMathFunction() || right_side->IsMathFunction())
+    return Create(left_side, right_side, op);
+
   CalculationCategory left_category = left_side->Category();
   CalculationCategory right_category = right_side->Category();
   DCHECK_NE(left_category, kCalcOther);

third_party/blink/web_tests/external/wpt/css/css-values/minmax-angle-serialize.html

@@ -20,6 +20,9 @@ test_valid_angle('max(1rad)', 'max(1rad)');
 test_valid_angle('max(1turn)', 'max(1turn)');
 test_valid_angle('max(1grad)', 'max(1grad)');
 
+test_valid_angle('calc(min(1deg) + min(2deg))', 'calc(min(1deg) + min(2deg))');
+test_valid_angle('calc(max(1deg) + max(2deg))', 'calc(max(1deg) + max(2deg))');
+
 // TODO(crbug.com/978682): Complete this test suite
 
 </script>