Navi A11y: Remove aria-pressed attribute on NTP background buttons

Bug: 938090
Change-Id: I0d4ef918d5eaf32b75f4122204fc0ffb208cae10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506655Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638385}

chrome/browser/resources/welcome/onboarding_welcome/ntp_background/nux_ntp_background.html

@@ -185,8 +185,6 @@
         <template is="dom-repeat" items="[[backgrounds_]]">
           <button
               active$="[[isSelectedBackground_(item, selectedBackground_)]]"
-              aria-pressed$="[[getAriaPressedValue_(item,
-                                                    selectedBackground_)]]"
               class="ntp-background-grid-button"
               on-click="onBackgroundClick_"
               on-keyup="onBackgroundKeyUp_"

chrome/browser/resources/welcome/onboarding_welcome/ntp_background/nux_ntp_background.js

@@ -54,14 +54,6 @@ Polymer({
     }
   },
 
-  /**
-   * @param {!nux.NtpBackgroundData} background
-   * @private
-   */
-  getAriaPressedValue_: function(background) {
-    return this.isSelectedBackground_(background).toString();
-  },
-
   /**
    * @return {boolean}
    * @private

chrome/test/data/webui/welcome/nux_ntp_background_test.js

@@ -97,11 +97,8 @@ cr.define('onboarding_ntp_background_test', function() {
 
       options[1].click();
       assertFalse(options[0].hasAttribute('active'));
-      assertEquals(options[0].getAttribute('aria-pressed'), 'false');
       assertTrue(options[1].hasAttribute('active'));
-      assertEquals(options[1].getAttribute('aria-pressed'), 'true');
       assertFalse(options[2].hasAttribute('active'));
-      assertEquals(options[2].getAttribute('aria-pressed'), 'false');
     });
 
     test('test setting the background when hitting next', function() {