Make shelf item can be dragged when context menu is opened.

ui/views/controls/menu/menu_runner.h

 // Copyright (c) 2012 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.
 
 #ifndef UI_VIEWS_CONTROLS_MENU_MENU_RUNNER_H_
 #define UI_VIEWS_CONTROLS_MENU_MENU_RUNNER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 71 matching lines @@
 
     // A child view is performing a drag-and-drop operation, so the menu should
     // stay open (even if it doesn't receive drag updated events). In this case,
     // the caller is responsible for closing the menu upon completion of the
     // drag-and-drop.
     NESTED_DRAG = 1 << 5,
 
     // Menu with fixed anchor position, so |MenuRunner| will not attempt to
     // adjust the anchor point. For example the context menu of shelf item.
     FIXED_ANCHOR = 1 << 6,
+
+    // Owner of the menu can be dragged after menu is created and dragging will
+    // close the menu. For example the shelf item can be dragged when the
+    // context menu of the item is opened.

[xiyuan, 2017/05/26 23:13:38]

nit: I would say something like

// Owner of the menu could be in the middle of a gesture when the menu
// opens and can use this flag to continue the gesture. For example,
// shelf uses the flag to continue dragging an item without lifting the
// finger after the context menu of the item is opened.

[minch1, 2017/06/01 16:42:28]

Done.

+    PRESERVE_CURRENT_GESTURE_FOR_OWNER = 1 << 7,
   };
 
   // Creates a new MenuRunner, which may use a native menu if available.
   // |run_types| is a bitmask of RunTypes. If provided,
   // |on_menu_closed_callback| is invoked when the menu is closed.
   // Note that with a native menu (e.g. on Mac), the ASYNC flag in |run_types|
   // may be ignored. See http://crbug.com/682544.
   MenuRunner(ui::MenuModel* menu_model,
              int32_t run_types,
              const base::Closure& on_menu_closed_callback = base::Closure());
@@ skipping 56 matching lines @@
 
  protected:
   DisplayChangeListener() {}
 };
 
 }  // namespace internal
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_MENU_MENU_RUNNER_H_