Implement PointerEvent#dx

sky/framework/sky-drawer.sky

 <!--
 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 -->
 <import src="animation/controller.sky" as="AnimationController" />
 <import src="animation/curves.sky" as="Curves" />
 <import src="sky-element/sky-element.sky" as="SkyElement" />
 <import src="sky-scrollable.sky" />
 
@@ skipping 30 matching lines @@
   </div>
 </template>
 <script>
 const kWidth = 256;
 const kMinAnimationDurationMS = 120;
 const kMaxAnimationDurationMS = 500;
 const kAnimationCurve = Curves.easeInOut;
 
 module.exports = class extends SkyElement {
   created() {
-    this.previousX_ = 0;
     this.position_ = 0;
     this.mask_ = null;
     this.content_ = null;
     this.animation_ = new AnimationController(this);
   }
 
   shadowRootReady() {
     this.mask_ = this.shadowRoot.getElementById('mask');
     this.content_ = this.shadowRoot.getElementById('content');
     this.position = -kWidth;
@@ skipping 56 matching lines @@
   updateAnimation(position) {
     this.position = position;
   }
 
   handleMaskClick() {
     this.close();
   }
 
   handlePointerDown(event) {
     this.animation_.stop();
-    this.previousX_ = event.x;
   }
 
   handlePointerMove(event) {
-    // TODO(abarth): Implement event.dx;
-    var deltaX = event.x - this.previousX_;
-    this.previousX_ = event.x;
-    this.position += deltaX;
+    this.position += event.dx;
   }
 
   handlePointerUp(event) {
     if (!this.animation_.isAnimating)
       this.settle_();
   }
 
   handlePointerCancel(event) {
     if (!this.animation_.isAnimating)
       this.settle_();
   }
 }.register();
 </script>
 </sky-element>