Added ARIA labels to use cases of Polymer paper-button-light that were using the alt property

Paper-button-light doesn't support the alt property, so aria-label should be used instead.
R=dmazzoni@chromium.org, fukumi@chromium.org

Tested: Manually using Jaws
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I8db2a1c399f41fafc577634062df37972a80a816
Reviewed-on: https://chromium-review.googlesource.com/890778Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534830}

chrome/browser/resources/settings/site_settings/site_details.html

@@ -66,7 +66,8 @@
           <div class="list-item" id="storage" hidden$="[[!storedData_]]">
             <div class="start">[[storedData_]]</div>
             <button is="paper-icon-button-light" class="icon-delete-gray"
-                on-tap="onConfirmClearStorage_" alt="$i18n{siteSettingsDelete}">
+                on-tap="onConfirmClearStorage_"
+                aria-label="$i18n{siteSettingsDelete}">
             </button>
           </div>
         </div>

chrome/browser/resources/settings/site_settings/site_list.html

@@ -93,7 +93,7 @@
             <button is="paper-icon-button-light" id="resetSite"
                 class="icon-delete-gray" on-tap="onResetButtonTap_"
                 hidden="[[shouldHideResetButton_(item, readOnlyList)]]"
-                alt="$i18n{siteSettingsActionReset}">
+                aria-label="$i18n{siteSettingsActionReset}">
             </button>
             <button is="paper-icon-button-light" id="actionMenuButton"
                 class="icon-more-vert" on-tap="onShowActionMenuTap_"

ui/webui/resources/cr_elements/cr_expand_button/cr_expand_button.html

@@ -26,8 +26,8 @@
     <div id="outer" on-tap="toggleExpand_">
       <div id="label" on-tap="toggleExpand_"><slot></slot></div>
       <button is="paper-icon-button-light" class$="[[iconName_(expanded)]]"
-          toggles active="{{expanded}}" disabled="[[disabled]]" alt="[[alt]]"
-          aria-active-attribute="aria-expanded"
+          toggles active="{{expanded}}" disabled="[[disabled]]"
+          aria-label$="[[alt]]" aria-active-attribute="aria-expanded"
           tabindex$="[[tabIndex]]">
       </button>
     </div>