DevTools: Support popover on timeline overview.

Source/devtools/front_end/timeline/timelinePanel.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 42 matching lines @@
 
 .timeline-records-list {
     flex: auto;
 }
 
 #timeline-overview-grid {
     background-color: rgb(255, 255, 255);
 }
 
 .timeline-overview-frames-mode #timeline-overview-grid,
-.timeline-overview-frames-mode .overview-grid-window-area,
 .timeline-overview-frames-mode .overview-grid-current-position {
     display: none;
 }
 
 #timeline-overview-grid .resources-dividers-label-bar {
     pointer-events: auto;
 }
 
 .timeline-overview-frames-mode .overview-grid-window,
 .timeline-overview-frames-mode .overview-grid-dividers-background {
@@ skipping 787 matching lines @@
 .timeline-gap {
     flex: none;
 }
 
 .timeline-filmstrip-preview {
     margin-top: 10px;
     max-width: 200px;
     max-height: 200px;
     cursor: pointer;
 }
+
+.timeline-overview-popover .frame .time {
+    display: none;
+}
+
+.timeline-overview-popover .frame .thumbnail img {
+    max-width: 200px;
+}