Add sky-drawer to the framework

sky/framework/animation/timer.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.
+-->
+<script>
+module.exports = class Timer {

[esprehn, 2015/01/29 19:03:57]

AnimationTimer, I expected this to do setTimeout from looking at the other code.

[abarth-chromium, 2015/01/29 19:16:45]

Good point.

+  constructor(delegate) {
+    this.delegate_ = delegate;
+    this.startTime_ = 0;
+    this.duration_ = 0;
+    this.animationId_ = 0;
+    Object.preventExtensions(this);
+  }
+
+  start(duration) {
+    if (this.animationId_)
+      this.stop();
+    this.duration_ = duration;
+    this.scheduleTick_();
+  }
+
+  stop() {
+    cancelAnimationFrame(this.animationId_);
+    this.startTime_ = 0;
+    this.duration_ = 0;
+    this.animationId_ = 0;
+  }
+
+  scheduleTick_() {
+    if (this.animationId_)
+      throw "Tick already scheduled.";

[esprehn, 2015/01/29 19:03:57]

new Error(...);

throwing a string is bad, you don't get a stack trace when you catch (e) { } it.

[abarth-chromium, 2015/01/29 19:16:45]

kk

+    this.animationId_ = requestAnimationFrame(this.tick_.bind(this));
+  }
+
+  tick_(timeStamp) {
+    this.animationId_ = 0;
+    if (!this.startTime_)
+      this.startTime_ = timeStamp;
+    var elapsedTime = timeStamp - this.startTime_;
+    var t = Math.max(0, Math.min(1, elapsedTime / this.duration_));
+    if (t < 1)
+      this.scheduleTick_();
+    else
+      this.stop();
+    this.delegate_.updateAnimation(t);
+  }
+};
+</script>