DevTools: Support popover on timeline overview.

Source/devtools/front_end/timeline/TimelinePanel.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 1801 matching lines @@
  * @constructor
  * @extends {WebInspector.TimelineOverviewBase}
  * @param {!WebInspector.TracingModel} tracingModel
  */
 WebInspector.TimelineFilmStripOverview = function(tracingModel)
 {
     WebInspector.TimelineOverviewBase.call(this);
     this._tracingModel = tracingModel;
     this._filmStripView = new WebInspector.FilmStripView();
     this._filmStripView.show(this.element);
+    this._lastIndex = -1;
+    this._lastElement = null;
 }
 
 WebInspector.TimelineFilmStripOverview.prototype = {
     /**
      * @override
      */
     update: function()
     {
         var model = this._tracingModel;
         this._filmStripModel = new WebInspector.FilmStripModel(model);
         this._filmStripView.setModel(this._filmStripModel, model.minimumRecordTime(), model.maximumRecordTime() - model.minimumRecordTime());
     },
 
     /**
      * @override
+     * @param {number} time
+     * @return {?Element}
+     */
+    popoverElement: function(time)
+    {
+        if (!this._filmStripModel.frames().length)

[caseq, 2015/06/16 14:14:49]

Is this guaranteed to always be called after update()?

[alph, 2015/06/17 09:17:08]

Guarded.

+            return null;
+        var index = this._filmStripView.frameIndexByTime(time);
+        console.assert(index >= 0);
+        if (index !== this._lastIndex) {
+            this._lastIndex = index;
+            this._lastElement = this._filmStripView.frameElementByIndex(index);
+            this._lastElement.appendChild(WebInspector.Widget.createStyleElement("timeline/timelinePanel.css"));
+        }
+        return this._lastElement;
+    },
+
+    /**
+     * @override
      */
     reset: function()
     {
         this._filmStripView.reset();
+        this._lastIndex = -1;
+        this._lastElement = null;
     },
 
     __proto__: WebInspector.TimelineOverviewBase.prototype
 }