Assert that convertToLength succeeds instead of returning Length(Undefined)

Source/core/css/resolver/StyleBuilderConverter.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
  * copyright notice, this list of conditions and the following disclaimer
  * in the documentation and/or other materials provided with the
  * distribution.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 28 matching lines @@
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     if (primitiveValue->isURI())
         return SVGURIReference::fragmentIdentifierFromIRIString(primitiveValue->getStringValue(), state.document());
     return String();
 }
 
 Length StyleBuilderConverter::convertLength(StyleResolverState& state, CSSValue* value)
 {
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     Length result = primitiveValue->convertToLength<FixedConversion | PercentConversion>(state.cssToLengthConversionData());
-    ASSERT(!result.isUndefined());
     result.setQuirk(primitiveValue->isQuirkValue());
     return result;
 }
 
 Length StyleBuilderConverter::convertLengthOrAuto(StyleResolverState& state, CSSValue* value)
 {
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     Length result = primitiveValue->convertToLength<FixedConversion | PercentConversion | AutoConversion>(state.cssToLengthConversionData());
-    ASSERT(!result.isUndefined());
     result.setQuirk(primitiveValue->isQuirkValue());
     return result;
 }
 
 Length StyleBuilderConverter::convertLengthSizing(StyleResolverState& state, CSSValue* value)
 {
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     switch (primitiveValue->getValueID()) {
     case CSSValueInvalid:
         return convertLength(state, value);
@@ skipping 96 matching lines @@
         return primitiveValue->computeLength<float>(state.cssToLengthConversionData().copyWithAdjustedZoom(1));
     return primitiveValue->computeLength<float>(state.cssToLengthConversionData());
 }
 
 SVGLength StyleBuilderConverter::convertSVGLength(StyleResolverState&, CSSValue* value)
 {
     return SVGLength::fromCSSPrimitiveValue(toCSSPrimitiveValue(value));
 }
 
 } // namespace WebCore