Length type Relative is now unused. Remove it.

Source/core/animation/css/CSSAnimatableValueFactory.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * 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
@@ skipping 71 matching lines @@
     case Intrinsic:
     case MinIntrinsic:
     case MinContent:
     case MaxContent:
     case FillAvailable:
     case FitContent:
         return AnimatableUnknown::create(CSSPrimitiveValue::create(length));
     case Undefined:
         return AnimatableUnknown::create(CSSValueNone);
     case ExtendToZoom: // Does not apply to elements.
-    case Relative: // Does not get used by interpolable properties.
         ASSERT_NOT_REACHED();
         return 0;
     }
     ASSERT_NOT_REACHED();
     return 0;
 }
 
 inline static PassRefPtr<AnimatableValue> createFromDouble(double value, AnimatableDouble::Constraint constraint = AnimatableDouble::Unconstrained)
 {
     return AnimatableDouble::create(value, constraint);
@@ skipping 339 matching lines @@
     case CSSPropertyZoom:
         return createFromDouble(style->zoom());
     default:
         RELEASE_ASSERT_WITH_MESSAGE(!CSSAnimations::isAnimatableProperty(property), "Web Animations not yet implemented: Create AnimatableValue from render style: %s", getPropertyNameString(property).utf8().data());
         ASSERT_NOT_REACHED();
         return 0;
     }
 }
 
 } // namespace WebCore