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

ui/views/controls/menu/menu_controller.h

Index: ui/views/controls/menu/menu_controller.h
diff --git a/ui/views/controls/menu/menu_controller.h b/ui/views/controls/menu/menu_controller.h
index 16ac2d4bd9c3a746d667f5c2c41e45d186e6fe61..06a7939683df0b52f0af0db20937b933658cc4f1 100644
--- a/ui/views/controls/menu/menu_controller.h
+++ b/ui/views/controls/menu/menu_controller.h
@@ -121,6 +121,10 @@ class VIEWS_EXPORT MenuController
   // 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_; }
@@ -667,6 +671,10 @@ class VIEWS_EXPORT MenuController
   // (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_;