Web Animations: Use PlaybackDirection enum in AnimationEffectTiming.idl

AnimationEffectTiming.idl and AnimationEffectTimingReadOnly.idl
now use
attribute PlaybackDirection direction;
for consistency with the spec.

https://w3c.github.io/web-animations/#the-animationeffecttiming-interface
https://w3c.github.io/web-animations/#the-animationeffecttimingreadonly-interface

BUG=716963

Review-Url: https://codereview.chromium.org/2856503002
Cr-Commit-Position: refs/heads/master@{#468295}

third_party/WebKit/Source/core/animation/AnimationEffectTiming.idl

@@ -13,6 +13,6 @@
     [RaisesException=Setter] attribute double iterationStart;
     [RaisesException=Setter] attribute unrestricted double iterations;
     [RaisesException=Setter] attribute (unrestricted double or DOMString) duration;
-    attribute DOMString direction;
+    attribute PlaybackDirection direction;
     [RaisesException=Setter] attribute DOMString easing;
 };

third_party/WebKit/Source/core/animation/AnimationEffectTimingReadOnly.idl

@@ -14,6 +14,6 @@
     readonly attribute double iterationStart;
     readonly attribute unrestricted double iterations;
     readonly attribute (unrestricted double or DOMString) duration;
-    readonly attribute DOMString direction;
+    readonly attribute PlaybackDirection direction;
     readonly attribute DOMString easing;
 };