[MD Bookmarks] Add keyboard navigation to sidebar.

chrome/browser/resources/md_bookmarks/folder_node.html

Index: chrome/browser/resources/md_bookmarks/folder_node.html
diff --git a/chrome/browser/resources/md_bookmarks/folder_node.html b/chrome/browser/resources/md_bookmarks/folder_node.html
index 2003e66387b9ee0b478caaa31086281f29c5d4c5..9770352b3c3be053cfbd3e35e820ea23ba86eee8 100644
--- a/chrome/browser/resources/md_bookmarks/folder_node.html
+++ b/chrome/browser/resources/md_bookmarks/folder_node.html
@@ -37,6 +37,7 @@
             calc(var(--node-depth, 0) * var(--padding-start-per-depth));
         cursor: pointer;
         height: 40px;
+        overflow: hidden;
         position: relative;
       }
 
@@ -82,7 +83,7 @@
     </style>
 
     <div id="container" class="v-centered" on-tap="selectFolder_"
-        draggable="[[!isRootFolder_(depth)]]"
+        draggable="[[!isRootFolder_(depth)]]" tabindex="getTabIndex_(focusable)"

[tsergeant, 2017/04/19 01:42:16]

needs $="[[]]"

[calamity, 2017/04/19 04:51:02]

Done.

         hidden="[[!isPositiveDepth_(depth)]]">
       <template is="dom-if" if="[[hasChildFolder_(item_.children)]]">
         <paper-icon-button id="arrow" icon="cr:arrow-drop-down"