DevTools: Support popover on timeline overview.

Source/devtools/front_end/components_lazy/filmStripView.css

 /*
  * 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.
  */
 
 .film-strip-view {
     overflow-x: auto;
     overflow-y: hidden;
     align-content: flex-start;
     min-height: 60px;
 }
 
+.film-strip-view.time-based .frame .time {
+    display: none;
+}
+
 .film-strip-view .label {
     margin: auto;
     font-size: 18px;
     color: #999;
 }
 
 .film-strip-view .frame {
     display: flex;
     flex-direction: column;
     align-items: center;
@@ skipping 28 matching lines @@
     max-width: 80px;
     max-height: 50px;
     pointer-events: none;
     border-right: solid 1px #eee;
 }
 
 .film-strip-view .frame .time {
     font-size: 10px;
     margin-top: 4px;
 }