[MR UI] Add a wrapper div to the sink list and search results in the MR dialog

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

Index: chrome/browser/resources/media_router/elements/media_router_container/media_router_container.css
diff --git a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.css b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.css
index 9ef29c9d991c79ad26e5a7efb10ec02c2adaa14d..fa6475c89542c00d22314f947a6c382f64d504d7 100644
--- a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.css
+++ b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.css
@@ -148,13 +148,15 @@ paper-menu {
   flex-grow: 1;
 }
 
+#search-results {
+  overflow-x: hidden;
+  overflow-y: auto;
+}
+
 #search-results-container {
   bottom: 0;
   left: 0;
   overflow-x: hidden;
-  /* overflow-y is set to auto when the results are actually displayed to allow
-   * scrolling. It is set to hidden by default so the scrollbar isn't displayed
-   * while animating. */
   overflow-y: hidden;
   position: absolute;
   right: 0;
@@ -196,6 +198,11 @@ paper-menu {
   position: relative;
 }
 
+#sink-list {
+  overflow-x: hidden;
+  overflow-y: auto;
+}
+
 .sink-name {
   min-width: 10%;
 }