Fix TimingAnimation rounding error issue (Take 2)

Summary:
This fixes a bug where the frames array can contain a duplicate entry at the end.
For example, suppose the duration is 1000.0 then it would create an array with the following:

```
[ 0,
  0.0010119824303159884,
  0.00391003997863186,
  0.00851330482578147,
  0.01466951184383165,
  0.022249135687575607,
  0.03114100006836614,
  0.041248932923769244,
  0.05248918022066495,
  0.06478838042267626,
  0.07808196049642172,
  0.09231285402599128,
  0.1074304693764467,
  0.12338985513375342,
  0.14015102395653428,
  0.15767840628626964,
  0.17594041329987542,
  0.1949090949486824,
  0.21455988464815853,
  0.23487142789035506,
  0.25582549864491233,
  0.27740701626433145,
  0.2996041891505173,
  0.3224088345090182,
  0.34581696665965683,
  0.36982983491413496,
  0.394455794287552,
  0.4197139228812336,
  0.44564199741037275,
  0.4723190090623474,
  0.5000000572130084,
  0.5276809909376533,
  0.5543580025896278,
  0.5802860771187669,
  0.6055442057124484,
  0.6301701650858652,
  0.6541830333403433,
  0.6775911654909819,
  0.7003958108494828,
  0.7225929837356684,
  0.7441745013550876,
  0.7651285721096447,
  0.785440115351841,
  0.8050909050513173,
  0.8240595867001241,
  0.84232159371373,
  0.8598489760434653,
  0.876610144866246,
  0.8925695306235529,
  0.9076871459740083,
  0.9219180395035779,
  0.9352116195773232,
  0.9475108197793346,
  0.9587510670762303,
  0.9688589999316335,
  0.9777508643124241,
  0.9853304881561681,
  0.9914866951742183,
  0.996089960021368,
  0.9989880175696839,
  1,
  1 ]
```

With this change, it now generates the following array:

```
[ 0,
  0.0010119824303159884,
  0.00391003997863186,
  0.00851330482578147,
  0.01466951184383165,
  0.022249135687575607,
  0.03114100006836614,
  0.041248932923769244,
  0.05248918022066495,
  0.06478838042267626,
  0.07808196049642172,
  0.09231285402599128,
  0.1074304693764467,
  0.12338985513375342,
  0.14015102395653428,
  0.15767840628626964,
  0.17594041329987542,
  0.1949090949486824,
  0.21455988464815853,
  0.23487142789035506,
  0.25582549864491233,
  0.27740701626433145,
  0.2996041891505173,
  0.3224088345090182,
  0.34581696665965683,
  0.36982983491413496,
  0.394455794287552,
  0.4197139228812336,
  0.44564199741037275,
  0.4723190090623474,
  0.5000000572130084,
  0.5276809909376533,
  0.5543580025896278,
  0.5802860771187669,
  0.6055442057124484,
  0.6301701650858652,
  0.6541830333403433,
  0.6775911654909819,
  0.7003958108494828,
  0.7225929837356684,
  0.7441745013550876,
  0.7651285721096447,
  0.785440115351841,
  0.8050909050513173,
  0.8240595867001241,
  0.84232159371373,
  0.8598489760434653,
  0.876610144866246,
  0.8925695306235529,
  0.9076871459740083,
  0.9219180395035779,
  0.9352116195773232,
  0.9475108197793346,
  0.9587510670762303,
  0.9688589999316335,
  0.9777508643124241,
  0.9853304881561681,
  0.9914866951742183,
  0.996089960021368,
  0.9989880175696839,
  1 ]
```

Note that the duplicate 1 at the end is now gone. This is because previously when it accumulated dt for 60 frames. dt wasn't quite exactly 1000, it was instead 999.9999999999999 and so didn't break out of the loop when it should have. This adds a tolerance so that it does break out of the loop.

Reviewed By: dimach1977

Differential Revision: D17828204

fbshipit-source-id: 4483303de852071436cf9a82e50296baf3392329

Author: Martin Sherburn

Libraries/Animated/src/__tests__/TimingAnimation-test.js

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @emails oncall+react_native
+ */
+
+'use strict';
+
+const TimingAnimation = require('../animations/TimingAnimation');
+
+describe('Timing Animation', () => {
+  it('should return array of 61 items', () => {
+    const timingAnim = new TimingAnimation({duration: 1000});
+    const config = timingAnim.__getNativeAnimationConfig();
+
+    expect(config.frames.length).toBe(61);
+    expect(config.frames[60]).toBe(1);
+    expect(config.frames[59]).toBeLessThan(1);
+  });
+
+  it('should cope with zero duration', () => {
+    const timingAnim = new TimingAnimation({duration: 0});
+    const config = timingAnim.__getNativeAnimationConfig();
+
+    expect(config.frames.length).toBe(1);
+    expect(config.frames[0]).toBe(1);
+  });
+});

Libraries/Animated/src/animations/TimingAnimation.js

@@ -66,8 +66,9 @@ class TimingAnimation extends Animation {
   __getNativeAnimationConfig(): any {
     const frameDuration = 1000.0 / 60.0;
     const frames = [];
-    for (let dt = 0.0; dt < this._duration; dt += frameDuration) {
-      frames.push(this._easing(dt / this._duration));
+    const numFrames = Math.round(this._duration / frameDuration);
+    for (let frame = 0; frame < numFrames; frame++) {
+      frames.push(this._easing(frame / numFrames));
     }
     frames.push(this._easing(1));
     return {