Implement Animation constructor

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

Index: third_party/WebKit/Source/core/animation/Animation.idl
diff --git a/third_party/WebKit/Source/core/animation/Animation.idl b/third_party/WebKit/Source/core/animation/Animation.idl
index 9f49ff93854b0f854314b240ebcec4e9435b7e5b..534b54d93a028bfd03d35d1fbe70ecc6f39ff4cd 100644
--- a/third_party/WebKit/Source/core/animation/Animation.idl
+++ b/third_party/WebKit/Source/core/animation/Animation.idl
@@ -33,9 +33,12 @@
 enum AnimationPlayState { "idle", "pending", "running", "paused", "finished" };
 
 [
+    Constructor(optional AnimationEffectReadOnly? effect = null, optional AnimationTimeline? timeline),
+    Exposed(Window WebAnimationsAPI),
+    ConstructorCallWith=ExecutionContext,
+    RaisesException=Constructor,
     ActiveScriptWrappable,
     DependentLifetime,
-    NoInterfaceObject,
 ] interface Animation : EventTarget {
     // TODO(suzyh): Make timeline mutable.
     [RuntimeEnabled=WebAnimationsAPI] attribute AnimationEffectReadOnly? effect;