[Wallpaper Picker] Cleaned UI artefacts in Surprise Me Mode.

In Surprise Me mode, changes are: 
- Top categories don't highlight anymore on Hover
- Online Wallpaper Attributes (author + url + thumbnail) are not displayed
- Selected Item Checkmark is not displayed
- "Add New" button is not highlighted on Hover and don't prompt user anymore.
- White Outline on thumbnails is not displayed.

Screenshot: http://i.imgur.com/UPhSQZS.jpg

Review URL: https://codereview.chromium.org/183853030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255379 0039d316-1c4b-4281-b951-d872f2087c98

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

@@ -66,7 +66,7 @@ body {
   height: 50px;
 }
 
-#categories-list > li:hover {
+#categories-list:not([disabled]) > li:hover {
   border-top-color: rgba(255, 255, 255, 0.4);
   cursor: pointer;
 }
@@ -159,7 +159,7 @@ body {
   width: 108px;
 }
 
-.image-picker [role=listitem]:hover {
+.image-picker:not([disabled]) [role=listitem]:hover {
   outline: 3px solid #f1f1f1;
   z-index: 1;
 }
@@ -196,6 +196,11 @@ body {
   width: 108px;
 }
 
+.image-picker[disabled]~.bottom-bar #online-wallpaper-attribute,
+.image-picker[disabled] .check {
+  visibility: hidden;
+}
+
 .image-picker[disabled],
 .image-picker-offline img:not([offline]) {
   -webkit-filter: grayscale(1);
@@ -302,7 +307,7 @@ body:not([custom]) [visibleif~='custom'] {
   content: url('../images/ui/add-wallpaper-thumbnail.png');
 }
 
-#add-new:hover img {
+.image-picker:not([disabled]) #add-new:hover img {
   content: url('../images/ui/add-wallpaper-thumbnail-hover.png');
 }
 

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

@@ -45,7 +45,9 @@ cr.define('wallpapers', function() {
         case Constants.WallpaperSourceEnum.AddNew:
           this.id = 'add-new';
           this.addEventListener('click', function(e) {
-            $('wallpaper-selection-container').hidden = false;
+            var checkbox = $('surprise-me').querySelector('#checkbox');
+            if (!checkbox.classList.contains('checked'))
+              $('wallpaper-selection-container').hidden = false;
           });
           break;
         case Constants.WallpaperSourceEnum.Custom: