cros: ChromeVox should announce "Wallpaper set successfully"

cvox.Api.speak may work but it requires goog.provide and goog.require.

Instead we could focus the checkmark and ChromeVox will announce its
aria-label.

This is a no-op for non-ChromeVox users.

Bug: 779449
Change-Id: I48de41156bb66e86d5e6051963f25be8355e12e0
Reviewed-on: https://chromium-review.googlesource.com/1187822
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585930}

chrome/browser/resources/chromeos/wallpaper_manager/css/wallpaper_manager.css

@@ -535,6 +535,10 @@ body.v2 {
   top: 8px;
 }
 
+.v2 .image-picker [role=listitem][selected] .check:focus {
+  outline: none;
+}
+
 .v2 .image-picker::-webkit-scrollbar-thumb {
   background: #888;
   display: none;

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.js

@@ -324,10 +324,15 @@ cr.define('wallpapers', function() {
     __proto__: Grid.prototype,
 
     /**
-     * The checkbox element.
+     * The checkbox element shown with the currently set wallpaper.
+     * @type {Object}
      */
     checkmark_: undefined,
 
+    get checkmark() {
+      return this.checkmark_;
+    },
+
     /**
      * ID of spinner delay timer.
      * @private
@@ -354,6 +359,7 @@ cr.define('wallpapers', function() {
      *     wallpaperInfo The information of the wallpaper to be set active.
      */
     activeItem_: undefined,
+
     set activeItem(activeItem) {
       if (this.activeItem_ != activeItem) {
         this.activeItem_ = activeItem;
@@ -603,6 +609,7 @@ cr.define('wallpapers', function() {
       this.checkmark_.classList.add('check');
       this.checkmark_.setAttribute(
           'aria-label', loadTimeData.getString('setSuccessfullyMessage'));
+      this.checkmark_.tabIndex = 0;
       this.dataModel = new ArrayDataModel([]);
       this.thumbnailList_ = new ArrayDataModel([]);
       this.useNewWallpaperPicker_ =

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js

@@ -1061,6 +1061,9 @@ WallpaperManager.prototype.onWallpaperChanged_ = function(
   $('wallpaper-set-by-message').textContent = '';
   $('wallpaper-grid').classList.remove('small');
 
+  if (this.useNewWallpaperPicker_)
+    this.wallpaperGrid_.checkmark.focus();
+
   // Disables daily refresh if user selects a non-daily wallpaper.
   if (activeItem && activeItem.source !== Constants.WallpaperSourceEnum.Daily)
     this.disableDailyRefresh_();