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

ui/views/controls/menu/menu_controller.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_CONTROLLER_H_
 #define UI_VIEWS_CONTROLS_MENU_MENU_CONTROLLER_H_
 
 #include <stddef.h>
 
 #include <list>
@@ skipping 103 matching lines @@
   void Cancel(ExitType type);
 
   // An alternative to Cancel(EXIT_ALL) that can be used with a OneShotTimer.
   void CancelAll() { Cancel(EXIT_ALL); }
 
   // When is_nested_run() this will add a delegate to the stack. The most recent
   // delegate will be notified. It will be removed upon the exiting of the
   // nested menu. Ownership is not taken.
   void AddNestedDelegate(internal::MenuControllerDelegate* delegate);
 
+  static void SetDoCancel(bool do_cancel) { do_cancel_ = do_cancel; }
+
+  static bool DoCancel() { return do_cancel_; }
+
   // Returns the current exit type. This returns a value other than EXIT_NONE if
   // the menu is being canceled.
   ExitType exit_type() const { return exit_type_; }
 
   // Returns the time from the event which closed the menu - or 0.
   base::TimeTicks closing_event_time() const { return closing_event_time_; }
 
   void set_is_combobox(bool is_combobox) { is_combobox_ = is_combobox; }
 
   // Various events, forwarded from the submenu.
@@ skipping 526 matching lines @@
   base::TimeTicks menu_start_time_;
 
   // If a mouse press triggered this menu, this will have its location (in
   // screen coordinates). Otherwise this will be (0, 0).
   gfx::Point menu_start_mouse_press_loc_;
 
   // Controls behavior differences between a combobox and other types of menu
   // (like a context menu).
   bool is_combobox_;
 
+  // In order to make item can be dragged after context menu is opened. Cannot
+  // cancel existing touch events.

[xiyuan, 2017/05/15 19:20:52]

Can we make the document from the perspective of menu? Mentioning dragging shelf
item etc does not make much sense in the context of menu. I would prefer
something like

  // Whether the menu |owner_| needs gesture events. When set to true
  // MenuController forwards unhandled gesture events to |owner_|.
  bool owner_needs_gesture_events_ = false;

Note the proposed |owner_needs_gesture_events_| is opposite of |do_cancel_|.

[minch1, 2017/05/16 22:13:39]

Done.

+  static bool do_cancel_;

[xiyuan, 2017/05/15 19:20:52]

Why this needs to be static? We already have a static getter for MenuController.
Can we make it a regular member and use the getter to access it?

[minch1, 2017/05/15 22:16:34]

But in shelf_view.cc where where we want to set this variable. We have no
MenuController instance yet. |active_instance_| returned by GetActiveInstance()
in MenuController is initialized in the Constructor. 

[xiyuan, 2017/05/15 22:41:10]

How about adding a new MenuRunner::RunTypes mask and MenuRunnerImpl sets this
flag when it sees the new RunTypes bit is set ?

[minch1, 2017/05/16 22:13:39]

Done.

+
   // Set to true if the menu item was selected by touch.
   bool item_selected_by_touch_;
 
   // During mouse event handling, this is the RootView to forward mouse events
   // to. We need this, because if we forward one event to it (e.g., mouse
   // pressed), subsequent events (like dragging) should also go to it, even if
   // the mouse is no longer over the view.
   MenuHostRootView* current_mouse_event_target_;
 
   // A mask of the EventFlags for the mouse buttons currently pressed.
   int current_mouse_pressed_state_;
 
 #if defined(USE_AURA)
   std::unique_ptr<MenuPreTargetHandler> menu_pre_target_handler_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(MenuController);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_MENU_MENU_CONTROLLER_H_