Web Animations API: Implement step-middle and steps(x, middle) timing functions.

Source/core/css/resolver/CSSToStyleMap.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 457 matching lines @@
             break;
         case CSSValueEaseOut:
             return CubicBezierTimingFunction::preset(CubicBezierTimingFunction::EaseOut);
             break;
         case CSSValueEaseInOut:
             return CubicBezierTimingFunction::preset(CubicBezierTimingFunction::EaseInOut);
             break;
         case CSSValueStepStart:
             return StepsTimingFunction::preset(StepsTimingFunction::Start);
             break;
+        case CSSValueStepMiddle:
+            return StepsTimingFunction::preset(StepsTimingFunction::Middle);
+            break;
         case CSSValueStepEnd:
             return StepsTimingFunction::preset(StepsTimingFunction::End);
             break;
         default:
             break;
         }
         return 0;
     }
 
     if (value->isCubicBezierTimingFunctionValue()) {
         CSSCubicBezierTimingFunctionValue* cubicTimingFunction = toCSSCubicBezierTimingFunctionValue(value);
         return CubicBezierTimingFunction::create(cubicTimingFunction->x1(), cubicTimingFunction->y1(), cubicTimingFunction->x2(), cubicTimingFunction->y2());
     } else if (value->isStepsTimingFunctionValue()) {
         CSSStepsTimingFunctionValue* stepsTimingFunction = toCSSStepsTimingFunctionValue(value);
-        return StepsTimingFunction::create(stepsTimingFunction->numberOfSteps(), stepsTimingFunction->stepAtStart());
+        return StepsTimingFunction::create(stepsTimingFunction->numberOfSteps(), stepsTimingFunction->stepAtPosition());
     }
 
     return 0;
 }
 
 void CSSToStyleMap::mapAnimationTimingFunction(CSSAnimationData* animation, CSSValue* value) const
 {
     RefPtr<TimingFunction> timingFunction = animationTimingFunction(value, true);
     if (timingFunction)
         animation->setTimingFunction(timingFunction);
@@ skipping 161 matching lines @@
         verticalRule = SpaceImageRule;
         break;
     default: // CSSValueRepeat
         verticalRule = RepeatImageRule;
         break;
     }
     image.setVerticalRule(verticalRule);
 }
 
 };