WebUI: cr-toast-manager, fix cr-button style when slotted

Bug: 1131871
Change-Id: Ic88e6fba9226ed273aa028ef8a489c0f6e8e583c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441008
Commit-Queue: Esmael Elmoslimany <aee@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Auto-Submit: Esmael Elmoslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812422}

ui/webui/resources/cr_elements/cr_toast/cr_toast_manager.html

@@ -32,9 +32,7 @@
     </style>
     <cr-toast id="toast" duration="[[duration]]">
       <div id="content" class="elided-text"></div>
-      <div id="slotted">
-        <slot></slot>
-      </div>
+      <slot id="slotted"></slot>
     </cr-toast>
   </template>
   <script src="cr_toast_manager.js"></script>