MD Settings: Prevent flash of subpage when collapsing section

chrome/browser/resources/settings/settings_page/settings_animated_pages.html

Index: chrome/browser/resources/settings/settings_page/settings_animated_pages.html
diff --git a/chrome/browser/resources/settings/settings_page/settings_animated_pages.html b/chrome/browser/resources/settings/settings_page/settings_animated_pages.html
index e7245d88615ec15ca946535f06e06607e9072941..7784476f63e20b651dd1b514aa4e8771ce0ddf8b 100644
--- a/chrome/browser/resources/settings/settings_page/settings_animated_pages.html
+++ b/chrome/browser/resources/settings/settings_page/settings_animated_pages.html
@@ -28,6 +28,11 @@
       neon-animated-pages ::content > .iron-selected {
         position: static;
       }
+
+      neon-animated-pages ::content > settings-subpage {
+        /* Ensure sub-pages are clipped when a section is collapsing. */
+        overflow: hidden;
+      }
     </style>
     <neon-animated-pages id="animatedPages" attr-for-selected="route-path"
         on-iron-select="onIronSelect_">