[MD Bookmarks] Make folder nodes extend their whole width.

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-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">
 
 <dom-module id="bookmarks-folder-node">
   <template>
     <style include="shared-style">
       :host {
+        --padding-left-per-depth: 30px;
         display: block;
       }
 
       .v-centered {
         align-items: center;
         display: flex;
         flex-direction: row;
       }
 
       .menu-label {
         -webkit-margin-start: 24px;
         color: var(--folder-inactive-color);
         font-weight: 500;
         overflow: hidden;
         text-overflow: ellipsis;
         white-space: nowrap;
       }
 
       #container {
         height: 40px;
       }
 
-      #descendants {
-        -webkit-padding-start: 40.5px;
-      }
-
       #folder-label {
         color: var(--secondary-text-color);
         cursor: pointer;
         flex-grow: 1;
         overflow: hidden;
       }
 
       :host([is-selected-folder]) .menu-label,
       :host([is-selected-folder]) #folder-label {
         color: var(--folder-active-color);
@@ skipping 20 matching lines @@
         <div class="menu-label">[[item.title]]</div>
       </div>
       <template is="dom-if" if="[[hasChildFolder_(item.children)]]">
         <paper-icon-button icon="[[getArrowIcon_(isClosed)]]"
             on-tap="toggleFolder_"></paper-icon-button>
       </template>
     </div>
     <div id="descendants" hidden$="[[isClosed]]">
       <template is="dom-repeat" items="[[item.children]]"
           filter="isFolder_" as="child">
-        <bookmarks-folder-node item-id="[[child]]">
+        <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>