[NTP] Fix 'Done' button tabindex for richer picker

Bug: 990789
Change-Id: I6d489a1f01397cdc611911dc9c5000a244648c05
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1737036
Commit-Queue: Kristi Park <kristipark@chromium.org>
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Auto-Submit: Kristi Park <kristipark@chromium.org>
Reviewed-by: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684093}

chrome/browser/resources/local_ntp/customize.js

@@ -868,7 +868,7 @@ customize.richerPicker_isOptionSelected = function() {
 customize.richerPicker_maybeToggleDone = function() {
   const enable = customize.richerPicker_isOptionSelected();
   $(customize.IDS.MENU_DONE).disabled = !enable;
-  $(customize.IDS.MENU_DONE).tabIndex = enable ? 1 : 0;
+  $(customize.IDS.MENU_DONE).tabIndex = enable ? 0 : -1;
 };
 
 /**