Web Animations API: Refactor IDL input conversion out of Animation

Source/core/animation/Timing.h

Index: Source/core/animation/Timing.h
diff --git a/Source/core/animation/Timing.h b/Source/core/animation/Timing.h
index fb2ef0921f2734ae3e161425a2b8be825c6db7e0..8aa2b58ff14fae0f99d9b7995a201f7a958f0cd0 100644
--- a/Source/core/animation/Timing.h
+++ b/Source/core/animation/Timing.h
@@ -59,13 +59,15 @@ struct Timing {
         , fillMode(FillModeAuto)
         , iterationStart(0)
         , iterationCount(1)
-        , iterationDuration(std::numeric_limits<double>::quiet_NaN())
+        , iterationDuration(initialIterationDuration())
         , playbackRate(1)
         , direction(PlaybackDirectionNormal)
         , timingFunction(LinearTimingFunction::create())
     {
     }
 
+    static double initialIterationDuration() { return std::numeric_limits<double>::quiet_NaN(); }
+
     void assertValid() const
     {
         ASSERT(std::isfinite(startDelay));