Set accessible name to the checkbox in the history item.

According to the ARIA spec, a checkbox must have a name, but in the
history page we are not giving a name to the item with role checkbox
but to its parent instead.

The cr-checkbox component can render its light-DOM children to a hidden
div used by the checkbox as accessible label container, we make use this
feature to fix the problem.

Bug: 1152721
Change-Id: Ia36bab94497caa60832d02876307f844744340a5
AX-relnotes: make checkboxes in history page ARIA-compliant.
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2584502Reviewed-by: John Lee <johntlee@chromium.org>
Commit-Queue: Jacobo Aragunde Pérez <jaragunde@igalia.com>
Cr-Commit-Position: refs/heads/master@{#836631}

chrome/browser/resources/history/history_item.html

@@ -166,8 +166,9 @@
               on-mousedown="onCheckboxClick_" on-keydown="onCheckboxClick_"
               on-change="onCheckboxChange_" class="no-label"
               hidden="[[selectionNotAllowed_]]"
-              disabled="[[selectionNotAllowed_]]"
-              aria-label$="[[getEntrySummary_(item)]]"></cr-checkbox>
+              disabled="[[selectionNotAllowed_]]">
+            [[getEntrySummary_(item)]]
+          </cr-checkbox>
         </div>
         <!-- ARIA hidden to avoid redundancy since timestamp is already part of
              |getEntrySummary_|. -->