DevTools: Fix first paint screenshot.

third_party/WebKit/Source/devtools/front_end/components_lazy/FilmStripModel.js

 /*
  * 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.
  */
 
 /**
  * @constructor
  * @param {!WebInspector.TracingModel} tracingModel
  * @param {number=} zeroTime
@@ skipping 53 matching lines @@
     {
         return this._zeroTime;
     },
 
     /**
      * @param {number} timestamp
      * @return {?WebInspector.FilmStripModel.Frame}
      */
     frameByTimestamp: function(timestamp)
     {
-        /**
-         * @param {number} timestamp
-         * @param {!WebInspector.FilmStripModel.Frame} frame
-         * @return {number}
-         */
-        function comparator(timestamp, frame)
-        {
-            return timestamp - frame.timestamp;
-        }
-        var index = this._frames.lowerBound(timestamp, comparator);
-        return index < this._frames.length ? this._frames[index] : null;
+        var index = this._frames.upperBound(timestamp, (timestamp, frame) => timestamp - frame.timestamp) - 1;
+        return index >= 0 ? this._frames[index] : null;
     }
 }
 
 /**
  * @constructor
  * @param {!WebInspector.FilmStripModel} model
  * @param {number} timestamp
  * @param {number} index
  */
 WebInspector.FilmStripModel.Frame = function(model, timestamp, index)
@@ skipping 46 matching lines @@
      * @return {!Promise<?string>}
      */
     imageDataPromise: function()
     {
         if (this._imageData || !this._snapshot)
             return Promise.resolve(this._imageData);
 
         return /** @type {!Promise<?string>} */ (this._snapshot.objectPromise());
     }
 }