Select the pointed item when drag operation starts.

ui/webui/resources/js/cr/ui/list.js

Index: ui/webui/resources/js/cr/ui/list.js
diff --git a/ui/webui/resources/js/cr/ui/list.js b/ui/webui/resources/js/cr/ui/list.js
index 240bd6e901033fe5a4739519fbf9e56efcd87a68..be30dff539fc62ce25537260711de15bcd239d51 100644
--- a/ui/webui/resources/js/cr/ui/list.js
+++ b/ui/webui/resources/js/cr/ui/list.js
@@ -314,6 +314,7 @@ cr.define('cr.ui', function() {
 
       this.addEventListener('dblclick', this.handleDoubleClick_);
       this.addEventListener('mousedown', handleMouseDown);
+      this.addEventListener('dragstart', handleDragStart, true);
       this.addEventListener('mouseup', this.handlePointerDownUp_);
       this.addEventListener('keydown', this.handleKeyDown);
       this.addEventListener('focus', this.handleElementFocus_, true);
@@ -1303,6 +1304,24 @@ cr.define('cr.ui', function() {
   }
 
   /**
+   * Dragstart event handler.
+   * If there is an item at starting position of drag operation and the item
+   * is not selected, select it.
+   * @this {List}
+   * @param {MouseEvent} e The event object for 'dragstart'.
+   */
+  function handleDragStart(e) {
+    var element = e.target.ownerDocument.elementFromPoint(e.clientX, e.clientY);
+    var target = this.getListItemAncestor(element);
+    var index = this.getIndexOfListItem(target);
+    if (index != -1) {
+      var isAlreadySelected = this.selectionModel_.getIndexSelected(index);
+      if (!isAlreadySelected)
+        this.selectionModel_.selectedIndex = index;
+    }
+  }
+
+  /**
    * Check if |start| or its ancestor under |root| is focusable.
    * This is a helper for handleMouseDown.
    * @param {!Element} start An element which we start to check.