[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 cb1ea0b46cfd9703b60f3ca75eb92236ad649fce..8f3a5ec7be1dcbfd1af4e426afe5139e48ede624 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,
 
@@ -74,6 +79,12 @@ Polymer({
         bookmarks.actions.changeFolderOpen(this.item.id, this.isClosed));
   },
 
+  /**
+   * @private
+   * @param {string} itemId
+   * @param {string} selectedFolder
+   * @return {boolean}
+   */
   computeIsSelected_: function(itemId, selectedFolder) {
     return itemId == selectedFolder;
   },
@@ -91,6 +102,19 @@ Polymer({
     return false;
   },
 
+  /** @private */
+  depthChanged_: function() {
+    this.style.setProperty('--node-depth', this.depth);

[tsergeant, 2017/03/08 23:26:17]

aaaaaahhhhhhh

(relatedly: CSS custom properties are still really poorly documented)

+  },
+
+  /**
+   * @private
+   * @return {number}
+   */
+  getChildDepth_: function() {
+    return this.depth + 1;
+  },
+
   /**
    * @param {string} itemId
    * @private