[NTP] Remove focus ring on disabled option

Removing focus ring when focusing on diabled options on "customize this
page" dialog.

Bug: 878769
Change-Id: I71466a87f4f1ea76022a09c072894d5ee9af1ed0
Reviewed-on: https://chromium-review.googlesource.com/1195932Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587802}

chrome/browser/resources/local_ntp/custom_backgrounds.css

@@ -126,6 +126,10 @@ html[dir=rtl] .bg-option-img {
   opacity: 0.28;
 }
 
+.bg-option.bg-option-disabled:focus {
+  outline: none;
+}
+
 .bg-option.bg-option-disabled:hover {
   background-color: transparent;
 }

chrome/browser/resources/local_ntp/custom_backgrounds.js

@@ -873,6 +873,7 @@ customBackgrounds.init = function(showErrorNotification) {
     editDialog.close();
   };
   editDialog.onclick = function(event) {
+    editDialog.classList.add(customBackgrounds.CLASSES.MOUSE_NAV);
     if (event.target === editDialog)
       editDialogInteraction();
   };