Fix decision of whether to drop y value for 2d translate

Spec requires dropping y value for 2d translate if it's zero (*). The
current implementation contains bug that:

1. It rounds the value before checking, which results in incorrect
   dropping of '0.1px'

2. It calls DoubleValue() on calc() without type checking, while
   DoubleValue() on calc() is meaningless when the calc() doesn't
   resolve to a simple numeric value (e.g., 1px - 1%). This results in
   incorrect dropping of some calc().

Both are fixed by this patch.

This is also a preparation for adding DCHECK in DoubleValue() to ensure
that it's called only when calc() can be resolved into a simple numeric
value.

Bug: 979895
Change-Id: Ie8b846729b91e55006485a25fab0b65533983eac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1692202Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675708}

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

@@ -144,4 +144,10 @@ double CSSMathFunctionValue::ClampToPermittedRange(double value) const {
   return IsNonNegative() && value < 0 ? 0 : value;
 }
 
+bool CSSMathFunctionValue::IsZero() const {
+  if (expression_->ResolvedUnitType() == UnitType::kUnknown)
+    return false;
+  return expression_->IsZero();
+}
+
 }  // namespace blink

third_party/blink/renderer/core/css/css_math_function_value.h

@@ -40,6 +40,8 @@ class CORE_EXPORT CSSMathFunctionValue : public CSSPrimitiveValue {
     return IsNonNegative() ? kValueRangeNonNegative : kValueRangeAll;
   }
 
+  bool IsZero() const;
+
   // TODO(crbug.com/979895): Make sure these functions are called only when
   // the math expression resolves into a double value.
   double DoubleValue() const;

third_party/blink/renderer/core/css/css_numeric_literal_value.h

@@ -18,6 +18,8 @@ class CORE_EXPORT CSSNumericLiteralValue : public CSSPrimitiveValue {
 
   CSSNumericLiteralValue(double num, UnitType type);
 
+  bool IsZero() const { return !DoubleValue(); }
+
   double DoubleValue() const { return num_; }
   double ComputeSeconds() const;
   double ComputeDegrees() const;

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

@@ -301,6 +301,11 @@ double CSSPrimitiveValue::GetDoubleValue() const {
                         : To<CSSNumericLiteralValue>(this)->DoubleValue();
 }
 
+bool CSSPrimitiveValue::IsZero() const {
+  return IsCalculated() ? To<CSSMathFunctionValue>(this)->IsZero()
+                        : To<CSSNumericLiteralValue>(this)->IsZero();
+}
+
 CSSPrimitiveValue::UnitType CSSPrimitiveValue::CanonicalUnitTypeForCategory(
     UnitCategory category) {
   // The canonical unit type is chosen according to the way

third_party/blink/renderer/core/css/css_primitive_value.h

@@ -228,6 +228,8 @@ class CORE_EXPORT CSSPrimitiveValue : public CSSValue {
   // Converts to a Length (Fixed, Percent or Calculated)
   Length ConvertToLength(const CSSToLengthConversionData&) const;
 
+  bool IsZero() const;
+
   // TODO(crbug.com/979895): Make sure this functions are called only when
   // applicable: on a numeric literal, or on a calc() that can be resolved into
   // a single value without extra context (e.g., CSSToLengthConversionData).

third_party/blink/renderer/core/css/properties/longhands/longhands_custom.cc

@@ -6685,7 +6685,7 @@ const CSSValue* Translate::ParseSingleValue(
   if (translate_y) {
     CSSValue* translate_z = css_property_parser_helpers::ConsumeLength(
         range, context.Mode(), kValueRangeAll);
-    if (translate_y->GetIntValue() == 0 && !translate_z)
+    if (translate_y->IsZero() && !translate_z)
       return list;
 
     list->Append(*translate_y);

third_party/blink/web_tests/external/wpt/css/css-transforms/parsing/translate-parsing-valid.html

@@ -18,7 +18,9 @@ test_valid_value("translate", "0px");
 test_valid_value("translate", "100%");
 
 test_valid_value("translate", "100px 0px", "100px");
+test_valid_value("translate", "100px 0.1px", "100px 0.1px");
 test_valid_value("translate", "100px 0%", "100px");
+test_valid_value("translate", "100px calc(10px - 10%)", "100px calc(10px - 10%)");
 test_valid_value("translate", "100px 200%");
 test_valid_value("translate", "100% 200px");