Web Animations: Reduce duplication of Timing defaults.

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..e05ed24f056be21fe8d474bd316225232e514836 100644
--- a/Source/core/animation/Timing.h
+++ b/Source/core/animation/Timing.h
@@ -53,6 +53,12 @@ struct Timing {
         PlaybackDirectionAlternateReverse
     };
 
+    static const Timing& defaults()
+    {
+        DEFINE_STATIC_LOCAL(Timing, timing, ());
+        return timing;
+    }
+
     Timing()
         : startDelay(0)
         , endDelay(0)