Devtools Animations: Support multiple frames in the animation timeline

Source/devtools/front_end/sdk/AnimationModel.js

Index: Source/devtools/front_end/sdk/AnimationModel.js
diff --git a/Source/devtools/front_end/sdk/AnimationModel.js b/Source/devtools/front_end/sdk/AnimationModel.js
index 573293b402253abe935d0204af9832f2782d23e9..89e066f349b2eddfee87a10a3f947473d72ea66c 100644
--- a/Source/devtools/front_end/sdk/AnimationModel.js
+++ b/Source/devtools/front_end/sdk/AnimationModel.js
@@ -159,7 +159,15 @@ WebInspector.AnimationModel.AnimationPlayer.prototype = {
      */
     startTime: function()
     {
-        return this._payload.startTime;
+        return this._startTime === undefined ? this._payload.startTime : this._startTime;
+    },
+
+    /**
+     * @param {number} startTime
+     */
+    updateStartTime: function(startTime)
+    {
+        this._startTime = startTime;
     },
 
     /**