[DevTools] Introduce a sidebar with a drop-down

third_party/WebKit/Source/devtools/front_end/ui/ListControl.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @template T
  * @interface
  */
 UI.ListDelegate = function() {};
 
@@ skipping 206 matching lines @@
     while (node && node.parentNodeOrShadowHost() !== this.element)
       node = node.parentNodeOrShadowHost();
     if (!node)
       return null;
     var element = /** @type {!Element} */ (node);
     var index = this._items.findIndex(item => this._itemToElement.get(item) === element);
     return index !== -1 ? this._items[index] : null;
   }
 
   /**
+   * @param {!T} item
+   * @return {?Element}
+   */
+  elementForItem(item) {
+    return this._itemToElement.get(item);
+  }
+
+  /**
    * @param {T} item
    * @param {boolean=} center
    */
   scrollItemIntoView(item, center) {
     var index = this._items.indexOf(item);
     if (index === -1)
       throw 'Attempt to scroll onto missing item';
     this._scrollIntoView(index, center);
   }
 
@@ skipping 424 matching lines @@
     this._firstIndex = firstIndex;
     this._lastIndex = lastIndex;
     this._topHeight = this._offsetAtIndex(firstIndex);
     this._topElement.style.height = this._topHeight + 'px';
     this._bottomHeight = totalHeight - this._offsetAtIndex(lastIndex);
     this._bottomElement.style.height = this._bottomHeight + 'px';
     this._renderedHeight = totalHeight;
     this.element.scrollTop = scrollTop;
   }
 };