WebUI: cr-checkbox, hide button inside checkbox from screenreaders

Bug: 870445
Change-Id: I9773698a1883f32b39adee9de7b1e7cfc2325c15
Reviewed-on: https://chromium-review.googlesource.com/c/1401455
Reviewed-by: Dan Beam <dbeam@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622253}
diff --git a/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.html b/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.html
index 64e279b4..603efbb 100644
--- a/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.html
+++ b/ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.html
@@ -125,7 +125,8 @@
     <!-- Mousing down then moving cursor out of this element should not trigger
          click on the parent. With <button> this works as expected, while <div>
          does not. -->
-    <button id="checkbox" tabindex="-1" on-focus="onButtonFocus_">
+    <button id="checkbox" tabindex="-1" on-focus="onButtonFocus_"
+        aria-hidden="true">
       <span id="checkmark"></span>
     </button>
     <div id="label-container"><slot></slot></div>