[refactored] dedupe to use named args

Summary: Continuation of #193

Reviewers: O2 Material Motion, O3 Material JavaScript platform reviewers, #material_motion, vietanh

Reviewed By: #material_motion, vietanh

Subscribers: vietanh

Tags: #material_motion

Differential Revision: http://codereview.cc/D3408

packages/core/src/operators/dedupe.ts

@@ -24,16 +24,20 @@ import {
   ObservableWithMotionOperators,
 } from '../types';
 
+export type DedupeArgs = {
+  areEqual?: EqualityCheck,
+};
+
 export interface MotionDeduplicable<T> {
-  dedupe(areEqual?: EqualityCheck): ObservableWithMotionOperators<T>;
+  dedupe(kwargs?: DedupeArgs): ObservableWithMotionOperators<T>;
 }
 
 export function withDedupe<T, S extends Constructor<ObservableWithFoundationalMotionOperators<T>>>(superclass: S): S & Constructor<MotionDeduplicable<T>> {
   return class extends superclass implements MotionDeduplicable<T> {
     /**
      * Ensures that every value dispatched is different than the previous one.
      */
-    dedupe(areEqual: EqualityCheck = deepEqual): ObservableWithMotionOperators<T> {
+    dedupe({ areEqual = deepEqual } = {}): ObservableWithMotionOperators<T> {
       return this._nextOperator({
         operation({ emit }) {
           let emitted = false;