Support animating <percentage> and <length-percentage> custom properties

third_party/WebKit/Source/core/animation/LengthInterpolationFunctions.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/animation/LengthInterpolationFunctions.h"
 
 #include "core/css/CSSCalculationValue.h"
 #include "core/css/CSSPrimitiveValue.h"
 #include "core/css/CSSToLengthConversionData.h"
 #include "platform/CalculationValue.h"
@@ skipping 195 matching lines @@
   const InterpolableList& interpolableList =
       toInterpolableList(interpolableValue);
   bool hasPercentage =
       CSSLengthNonInterpolableValue::hasPercentage(nonInterpolableValue);
 
   CSSCalcExpressionNode* rootNode = nullptr;
   CSSPrimitiveValue* firstValue = nullptr;
 
   for (size_t i = 0; i < CSSPrimitiveValue::LengthUnitTypeCount; i++) {
     double value = toInterpolableNumber(*interpolableList.get(i)).value();
-    if (value == 0 ||
-        (i == CSSPrimitiveValue::UnitTypePercentage && !hasPercentage)) {
+    if (value == 0 &&

[suzyh_UTC10 (ex-contributor), 2017/02/17 04:59:59]

Although this is a tiny bug fix, I'd prefer to see it in its own patch with a
dedicated test.

[alancutter (OOO until 2018), 2017/02/19 23:38:58]

This bug is unreachable without this change.

+        (i != CSSPrimitiveValue::UnitTypePercentage || !hasPercentage)) {
       continue;
     }
     CSSPrimitiveValue* currentValue =
         CSSPrimitiveValue::create(value, indexToUnitType(i));
 
     if (!firstValue) {
       DCHECK(!rootNode);
       firstValue = currentValue;
       continue;
     }
     CSSCalcExpressionNode* currentNode =
         CSSCalcValue::createExpressionNode(currentValue);
     if (!rootNode) {
       rootNode = CSSCalcValue::createExpressionNode(firstValue);
     }
     rootNode =
         CSSCalcValue::createExpressionNode(rootNode, currentNode, CalcAdd);
   }
 
   if (rootNode) {
     return CSSPrimitiveValue::create(CSSCalcValue::create(rootNode));
   }
   if (firstValue) {
     return firstValue;
   }
   return CSSPrimitiveValue::create(0, CSSPrimitiveValue::UnitType::Pixels);
 }
 
 }  // namespace blink