[MD Bookmarks] Add keyboard navigation to sidebar.

chrome/browser/resources/md_bookmarks/folder_node.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-a11y-keys-behavior/iron-a11y-keys-behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 <link rel="import" href="chrome://bookmarks/actions.html">
 <link rel="import" href="chrome://bookmarks/icons.html">
 <link rel="import" href="chrome://bookmarks/shared_style.html">
 <link rel="import" href="chrome://bookmarks/store_client.html">
@@ skipping 19 matching lines @@
         overflow: hidden;
         text-overflow: ellipsis;
         white-space: nowrap;
       }
 
       #container {
         -webkit-padding-start:
             calc(var(--node-depth, 0) * var(--padding-start-per-depth));
         cursor: pointer;
         height: 40px;
+        overflow: hidden;
         position: relative;
       }
 
       #folder-label {
         -webkit-padding-end: 8px;
         color: var(--secondary-text-color);
         flex-grow: 1;
         overflow: hidden;
       }
 
@@ skipping 25 matching lines @@
       #arrow[is-open] {
         transform: initial;
       }
 
       [no-children] {
         -webkit-padding-start: 52px; /* The width of the arrow and its margin */
       }
     </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"
             is-open$="[[!isClosed_]]" on-tap="toggleFolder_" tabindex="-1">
         </paper-icon-button>
       </template>
       <div id="folder-label" class="v-centered">
         <iron-icon icon="[[getFolderIcon_(isSelectedFolder_)]]"
             no-children$="[[!hasChildFolder_(item_.children)]]">
         </iron-icon>
         <div class="menu-label">[[item_.title]]</div>
       </div>
     </div>
     <div id="descendants" hidden$="[[isClosed_]]">
       <template is="dom-repeat"
           items="[[item_.children]]"
           as="child"
           filter="isFolder_">
         <bookmarks-folder-node item-id="[[child]]"
             depth="[[getChildDepth_(depth)]]">
         </bookmarks-folder-node>
       </template>
     </div>
   </template>
   <script src="chrome://bookmarks/folder_node.js"></script>
 </dom-module>