Animation: Remove ASSERT_NOT_REACHED from LengthStyleInterpolation

Source/core/animation/LengthStyleInterpolation.cpp

 // Copyright 2014 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 "config.h"
 #include "core/animation/LengthStyleInterpolation.h"
 
 #include "core/css/CSSCalculationValue.h"
 #include "core/css/resolver/StyleBuilder.h"
 
@@ skipping 77 matching lines @@
     unsigned unitTypeCount = 0;
     for (size_t i = 0; i < CSSPrimitiveValue::LengthUnitTypeCount; i++) {
         const InterpolableNumber* subType = toInterpolableNumber(listOfTypes->get(i));
         if (subType->value()) {
             unitTypeCount++;
         }
     }
 
     switch (unitTypeCount) {
     case 0:
-        ASSERT_NOT_REACHED();
+        // TODO: this case should never be reached. This issue should be fixed once we have multiple interpolators.
+        return CSSPrimitiveValue::create(0, CSSPrimitiveValue::CSS_PX);
     case 1:
         for (size_t i = 0; i < CSSPrimitiveValue::LengthUnitTypeCount; i++) {
             const InterpolableNumber *subValueType = toInterpolableNumber(listOfTypes->get(i));
             if (subValueType->value()) {
                 double value = toInterpolableNumber(listOfValues->get(i))->value();
                 if (range == ValueRangeNonNegative && value < 0)
                     value = 0;
                 return CSSPrimitiveValue::create(value, toUnitType(i));
             }
         }
         ASSERT_NOT_REACHED();
     default:
         return CSSPrimitiveValue::create(CSSCalcValue::create(constructCalcExpression(nullptr, listOfValuesAndTypes, 0), range));
     }
 }
 
 void LengthStyleInterpolation::apply(StyleResolverState& state) const
 {
     StyleBuilder::applyProperty(m_id, state, interpolableValueToLength(m_cachedValue.get(), m_range).get());
 }
 
 void LengthStyleInterpolation::trace(Visitor* visitor)
 {
     StyleInterpolation::trace(visitor);
 }
 
 }