MD Settings: Prevent flash of subpage when collapsing section

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

 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/cr/ui.html">
 <link rel="import" href="chrome://resources/html/cr/ui/focus_outline_manager.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/fade-in-animation.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/fade-out-animation.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/slide-from-left-animation.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/slide-from-right-animation.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/animations/slide-left-animation.html">
@@ skipping 10 matching lines @@
         display: block;
       }
 
       neon-animated-pages {
         position: static;
       }
 
       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_">
       <content select="*"></content>
     </neon-animated-pages>
   </template>
   <script src="settings_animated_pages.js"></script>
 </dom-module>