[MR UI] Make paper-items the only selectable elements in cast modes list

chrome/browser/resources/media_router/elements/media_router_container/media_router_container.html

Index: chrome/browser/resources/media_router/elements/media_router_container/media_router_container.html
diff --git a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.html b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.html
index de948ff6a9a7454231aad55dccf7a9aa6012d675..6234156c2c1ffaa18fe5be2aacd6c43324972e34 100644
--- a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.html
+++ b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.html
@@ -57,7 +57,8 @@
     </media-router-header>
     <div id="content">
       <template is="dom-if" if="[[!computeCastModeListHidden_(currentView_)]]">
-        <paper-menu id="cast-mode-list" role="presentation">
+        <paper-menu id="cast-mode-list" role="presentation"
+            selectable="paper-item">
           <template is="dom-repeat" id="defaultCastModeList"
               items="[[computeDefaultCastModeList_(castModeList)]]">
             <paper-item on-tap="onCastModeClick_">