Devtools Animations: Add cubic bezier easing editor for animations

Source/devtools/front_end/elements/BezierUI.js

 // Copyright (c) 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.
 
 /**
  * @constructor
  * @param {number} width
  * @param {number} height
  * @param {number} marginTop
  * @param {number} controlPointRadius
@@ skipping 99 matching lines @@
     var height = WebInspector.AnimationUI.Options.AnimationHeight;
     var pathBuilder = ["M", 0, height];
     const sampleSize = 1 / 40;
 
     var prev = bezier.evaluateAt(0);
     for (var t = sampleSize; t < 1 + sampleSize; t += sampleSize) {
         var current = bezier.evaluateAt(t);
         var slope = (current.y - prev.y) / (current.x - prev.x);
         var weightedX = prev.x * (1 - t) + current.x * t;
         slope = Math.tanh(slope / 1.5); // Normalise slope
+        // TODO(samli): Workaround for v8 bug https://code.google.com/p/v8/issues/detail?id=3495
+        if (isNaN(slope))
+            slope = 1;
         pathBuilder = pathBuilder.concat(["L", (weightedX * width).toFixed(2), (height - slope * height).toFixed(2) ]);
         prev = current;
     }
     pathBuilder = pathBuilder.concat(["L", width.toFixed(2), height, "Z"]);
     path.setAttribute("d", pathBuilder.join(" "));
 }