history: make checkboxes always visible (instead of just when hovered).

chrome/browser/resources/history/history.css

 /* Copyright (c) 2012 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. */
 
 html[dir='rtl'] body.uber-frame > .page {
   -webkit-margin-end: 0;
 }
 
 body.uber-frame > .page.big-topbar-page {
   padding-top: 78px;
@@ skipping 329 matching lines @@
   max-width: 90px;
   min-width: -webkit-min-content;
   overflow: hidden;
   text-overflow: ellipsis;
   white-space: nowrap;
 }
 
 .entry input[type='checkbox'] {
   -webkit-margin-end: 6px;
   line-height: 1em;
-  margin-top: 2px;
   min-width: 13px;
+  top: 0;
 }
 
 <if expr="not is_android">
-/* Checkboxes are shown when checked or focused, or when the entry is hovered.
- * Fade in on focus, but not on hover, because it makes the UI feel laggy. */
-.site-domain-wrapper input[type=checkbox]:not(:checked),
-.entry input[type='checkbox']:not(:checked) {
-  opacity: 0;
-}
-
 .site-domain-wrapper:hover input[type='checkbox'],
+.site-domain-wrapper input[type='checkbox']:checked,
 .site-domain-wrapper input[type='checkbox']:focus,
 .entry-box:hover input[type='checkbox'],
+.entry-box input[type='checkbox']:checked,
 .entry-box input[type='checkbox']:focus {
-  opacity: 1;
-}
-
-.site-domain-wrapper input[type='checkbox']:focus,
-.entry-box input[type='checkbox']:focus {
-  -webkit-transition: opacity 150ms;
+  border-color: rgba(0, 0, 0, .5);
 }
 
 .filter-status {
   -webkit-margin-start: 10px;
 }
 
 .filter-status > div {
   -webkit-flex: 0 0 auto;
   -webkit-transition: background-color 150ms;
   border-radius: 3px;
@@ skipping 39 matching lines @@
   background: url('../ssl/images/roadblock.png');
   background-size: 30%;
 }
 
 .blocked-indicator .title {
   color: rgb(151, 156, 160);
 }
 </if>
 
 .entry-box {
-  background-color: none;
+  -webkit-padding-start: 6px;
+  border-radius: 2px;
 }
 
 .entry-box:hover,
 .entry-box.contains-focus {
-  background-color: rgb(252, 252, 252);
-  border-radius: 2px;
+  background-color: rgba(0, 0, 0, .05);
 }
 
 .entry-box-container {
   display: -webkit-flex;
 }
 
 .entry .visit-entry {
   display: -webkit-flex;
   min-width: 0;
 }
@@ skipping 175 matching lines @@
   background-image: url(../../../../ui/webui/resources/images/phone_small.png);
   background-position: 14px center;
   padding-left: 43px;
 }
 
 #action-menu[data-devicetype='tablet']::before {
   background-image: url(../../../../ui/webui/resources/images/tablet_small.png);
   background-position: 17px center;
   padding-left: 49px;
 }