[Bluetooth] make ChromeVox announce device row once.

Added a top level property/attribute to bluetooth_device_list_item for
an explicit aria-label and put aria-hidden on the div text to avoid
repeating.

Bug: 1007100
Change-Id: Ie2b910c3b1652c1929f8c223fc68d94a66ac2d6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1876910Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: James Vecore <vecore@google.com>
Cr-Commit-Position: refs/heads/master@{#708835}

chrome/browser/resources/settings/bluetooth_page/bluetooth_device_list_item.html

@@ -24,7 +24,7 @@
       <iron-icon id="deviceIcon" icon="[[getDeviceIcon_(device)]]">
       </iron-icon>
       <div class="middle">
-        <div class="name" connected$="[[device.connected]]">
+        <div class="name" connected$="[[device.connected]]" aria-hidden="true">
           [[getDeviceName_(device)]]
         </div>
         <div class="state secondary" connected$="[[device.connected]]"

chrome/browser/resources/settings/bluetooth_page/bluetooth_device_list_item.js

@@ -19,6 +19,17 @@ Polymer({
     device: {
       type: Object,
     },
+
+    /**
+     * Uses getDeviceName_ as a label for a11y. It will be added as an
+     * attribute on this top-level bluetooth-device-list-item.
+     */
+    ariaLabel: {
+      type: String,
+      notify: true,
+      reflectToAttribute: true,
+      computed: 'getDeviceName_(device)',
+    },
   },
 
   /**