bluetooth: Add characteristic list to DeviceDetailsPage in internals page.

chrome/browser/resources/bluetooth_internals/expandable_list.js

Index: chrome/browser/resources/bluetooth_internals/expandable_list.js
diff --git a/chrome/browser/resources/bluetooth_internals/expandable_list.js b/chrome/browser/resources/bluetooth_internals/expandable_list.js
index e2d3be74e68da6c1f6b062d33d320f431c75e9c4..bbb8bcbeae01d2b3d6e5211f5efde02a24fb2a85 100644
--- a/chrome/browser/resources/bluetooth_internals/expandable_list.js
+++ b/chrome/browser/resources/bluetooth_internals/expandable_list.js
@@ -31,7 +31,7 @@ cr.define('expandable_list', function() {
       this.briefContent_ = document.createElement('div');
       this.briefContent_.classList.add('brief-content');
       this.briefContent_.addEventListener(
-          'click', this.toggleExpand_.bind(this));
+          'click', this.onExpand_.bind(this));
       this.appendChild(this.briefContent_);
 
       this.expandedContent_ = document.createElement('div');
@@ -40,11 +40,17 @@ cr.define('expandable_list', function() {
     },
 
     /**
+     * Called when the list item is expanded or collapsed.
+     * @param {boolean} expanded
+     */
+    onExpandInternal: function(expanded) {},
+
+    /**
      * Toggles the expanded class on the item.
      * @private
      */
-    toggleExpand_: function() {
-      this.classList.toggle('expanded');
+    onExpand_: function() {
+      this.onExpandInternal(this.classList.toggle('expanded'));
     },
   };
 
@@ -111,6 +117,14 @@ cr.define('expandable_list', function() {
     },
 
     /**
+     * Gets the loading state of the list. Returns true if the list is loading.
+     * @return {boolean}
+     */
+    isLoading: function() {
+      return !this.spinner_.hidden;
+    },
+
+    /**
      * Updates the display state of the empty message. If there are no items in
      * the data model, the empty message is displayed.
      */