Web Animations API: Start implementation of timing input objects.

Source/core/animation/ElementAnimation.idl

Index: Source/core/animation/ElementAnimation.idl
diff --git a/Source/core/animation/ElementAnimation.idl b/Source/core/animation/ElementAnimation.idl
index 8bbbce7e0e2c61ee3bc645135dd6d9d3626779a3..a13aef12f84bd1b03dc4a45dc92eafd2528d972d 100644
--- a/Source/core/animation/ElementAnimation.idl
+++ b/Source/core/animation/ElementAnimation.idl
@@ -27,9 +27,10 @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
-
 [
     RuntimeEnabled=WebAnimationsAPI,
 ] partial interface Element {
-    Animation animate(sequence<Dictionary> keyframes, optional double duration);
+    Animation animate(sequence<Dictionary> keyframes, Dictionary timingInput);
+    Animation animate(sequence<Dictionary> keyframes, double timingInput);
+    Animation animate(sequence<Dictionary> keyframes);
 };