Fix zoom handling in CSSMathFunctionValue::Create(length, zoom)

This patch fixes a regression introduced by crrev.com/c/1744799.

Before the regression, the creator divides the pixel value of the length
by the zooming after. The above patch incorrectly changed that into
multiplication, which is the regression.

This patch changes that back into a division.

Bug: 999875
Change-Id: Ic5f07c2af52cdc94bde8b355e5c30a7f01c0a49c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1783638
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@{#693131}

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

@@ -41,7 +41,7 @@ CSSMathFunctionValue* CSSMathFunctionValue::Create(
 CSSMathFunctionValue* CSSMathFunctionValue::Create(const Length& length,
                                                    float zoom) {
   DCHECK(length.IsCalculated());
-  auto calc = length.GetCalculationValue().Zoom(zoom);
+  auto calc = length.GetCalculationValue().Zoom(1.0 / zoom);
   return Create(CSSMathExpressionNode::Create(*calc), calc->GetValueRange());
 }
 

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

@@ -8,6 +8,7 @@
 #include "third_party/blink/renderer/core/css/css_math_expression_node.h"
 #include "third_party/blink/renderer/core/css/css_math_function_value.h"
 #include "third_party/blink/renderer/core/css/css_numeric_literal_value.h"
+#include "third_party/blink/renderer/core/css/css_to_length_conversion_data.h"
 
 namespace blink {
 namespace {
@@ -78,5 +79,28 @@ TEST(CSSPrimitiveValueTest, IsResolution) {
   EXPECT_TRUE(Create({5.0, UnitType::kDotsPerCentimeter})->IsResolution());
 }
 
+// https://crbug.com/999875
+TEST(CSSPrimitiveValueTest, Zooming) {
+  // Tests that the conversion CSSPrimitiveValue -> Length -> CSSPrimitiveValue
+  // yields the same value under zooming.
+
+  UnitValue a = {100, UnitType::kPixels};
+  UnitValue b = {10, UnitType::kPercentage};
+  CSSPrimitiveValue* original = CreateAddition(a, b);
+
+  CSSToLengthConversionData conversion_data;
+  conversion_data.SetZoom(0.5);
+
+  Length length = original->ConvertToLength(conversion_data);
+  EXPECT_TRUE(length.IsCalculated());
+  EXPECT_EQ(50.0, length.GetPixelsAndPercent().pixels);
+  EXPECT_EQ(10.0, length.GetPixelsAndPercent().percent);
+
+  CSSPrimitiveValue* converted =
+      CSSPrimitiveValue::CreateFromLength(length, conversion_data.Zoom());
+  EXPECT_TRUE(converted->IsMathFunctionValue());
+  EXPECT_EQ("calc(10% + 100px)", converted->CustomCSSText());
+}
+
 }  // namespace
 }  // namespace blink