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

chrome/browser/resources/md_bookmarks/folder_node.js

Index: chrome/browser/resources/md_bookmarks/folder_node.js
diff --git a/chrome/browser/resources/md_bookmarks/folder_node.js b/chrome/browser/resources/md_bookmarks/folder_node.js
index b88183d0f1a61dbc75a4212b6403d92ba52908cd..8b2ac66b902d1ec02d964429635f6fdf6e22fe16 100644
--- a/chrome/browser/resources/md_bookmarks/folder_node.js
+++ b/chrome/browser/resources/md_bookmarks/folder_node.js
@@ -15,6 +15,11 @@ Polymer({
       observer: 'updateFromStore',
     },
 
+    depth: {
+      type: Number,
+      observer: 'depthChanged_',
+    },
+
     /** @type {BookmarkNode} */
     item_: Object,
 
@@ -78,10 +83,10 @@ Polymer({
   },
 
   /**
+   * @private
    * @param {string} itemId
    * @param {string} selectedFolder
    * @return {boolean}
-   * @private
    */
   computeIsSelected_: function(itemId, selectedFolder) {
     return itemId == selectedFolder;
@@ -99,6 +104,19 @@ Polymer({
     return false;
   },
 
+  /** @private */
+  depthChanged_: function() {
+    this.style.setProperty('--node-depth', this.depth.toString());
+  },
+
+  /**
+   * @private
+   * @return {number}
+   */
+  getChildDepth_: function() {
+    return this.depth + 1;
+  },
+
   /**
    * @param {string} itemId
    * @private