NearbyShare: Add aria labels to NearbyPageTemplate buttons

Add aria-labels to buttons for improved a11y experience with
NearbyShare onboarding page.

Bug: 1148456
Test: Local
Change-Id: I706d9c28c0947ff40432f4c932846a1748224193
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545194Reviewed-by: James Vecore <vecore@google.com>
Commit-Queue: Jimmy Gong <jimmyxgong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828600}

chrome/browser/resources/nearby_share/shared/nearby_onboarding_page.html

@@ -53,7 +53,8 @@
         cancel-button-event-name="close">
       <div id=center-content slot="content">
         <iron-icon id="splash-image-column"
-            icon="nearby-images:nearby-onboarding-splash">
+            icon="nearby-images:nearby-onboarding-splash"
+            aria-hidden="true">
         </iron-icon>
         <div id="device-name-column">
           <cr-input label="$i18n{nearbyShareOnboardingPageDeviceName}"

chrome/browser/resources/nearby_share/shared/nearby_page_template.html

@@ -63,19 +63,20 @@
       <div id="actions">
         <template is="dom-if" if="[[utilityButtonLabel]]">
           <cr-button id="utilityButton" class="cancel-button"
-              on-click="onUtilityClick_">
+              on-click="onUtilityClick_" aria-label="[[utilityButtonLabel]]">
             [[utilityButtonLabel]]
           </cr-button>
         </template>
         <template is="dom-if" if="[[cancelButtonLabel]]">
           <cr-button id="cancelButton" class="cancel-button"
-              on-click="onCancelClick_">
+              on-click="onCancelClick_" aria-label="[[cancelButtonLabel]]">
             [[cancelButtonLabel]]
           </cr-button>
         </template>
         <template is="dom-if" if="[[actionButtonLabel]]">
           <cr-button id="actionButton" class="action-button"
-              on-click="onActionClick_" disabled="[[actionDisabled]]">
+              on-click="onActionClick_" disabled="[[actionDisabled]]"
+              aria-label="[[actionButtonLabel]]">
             [[actionButtonLabel]]
           </cr-button>
         </template>