a11y: Hide labels for Settings power page

Hide the labels so the power source is one stop in ChromeVox.

Video: http://crbug/1031355#c9

Fixed: 1031355
Change-Id: I4878e916fb44229a9ef195b616a1cd21a4103624
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463331Reviewed-by: Regan Hsu <hsuregan@chromium.org>
Commit-Queue: Gavin Williams <gavinwill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815834}

chrome/browser/resources/settings/chromeos/device_page/power.html

@@ -26,13 +26,14 @@
     </style>
     <div id="powerSourceRow" class="cr-row first"
         hidden$="[[!batteryStatus_.present]]">
-      <div class="flex cr-padded-text" id="powerSourceLabelDiv">
-        <div>[[powerSourceLabel_]]</div>
-        <div class="secondary">[[batteryStatus_.statusText]]</div>
+      <div class="flex cr-padded-text" aria-hidden="true">
+        <div id="powerSourceLabel">[[powerSourceLabel_]]</div>
+        <div id="batteryStatus" class="secondary">[[batteryStatus_.statusText]]</div>
       </div>
       <select id="powerSource" class="md-select"
           hidden$="[[!showPowerSourceDropdown_]]"
-          aria-labelledby="powerSourceLabelDiv"
+          aria-labelledby="powerSourceLabel"
+          aria-describedby="batteryStatus"
           on-change="onPowerSourceChange_"
           deep-link-focus-id$="[[Setting.kPowerSource]]">
         <option value="" selected="[[isEqual_('', selectedPowerSourceId_)]]">
@@ -45,7 +46,9 @@
           </option>
         </template>
       </select>
-      <div hidden$="[[showPowerSourceDropdown_]]">
+      <div hidden$="[[showPowerSourceDropdown_]]"
+          aria-labelledby="powerSourceLabel"
+          aria-describedby="batteryStatus">
         [[powerSourceName_]]
       </div>
     </div>