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

ui/views/controls/menu/menu_host.h

Index: ui/views/controls/menu/menu_host.h
diff --git a/ui/views/controls/menu/menu_host.h b/ui/views/controls/menu/menu_host.h
index 484b90889320a3c7c05724aacfbab234382db741..5c3aad19f4ba60da12c09d96ce63602f1bb5f8a7 100644
--- a/ui/views/controls/menu/menu_host.h
+++ b/ui/views/controls/menu/menu_host.h
@@ -46,14 +46,15 @@ class MenuHost : public Widget {
   void InitMenuHost(Widget* parent,
                     const gfx::Rect& bounds,
                     View* contents_view,
-                    bool do_capture);
+                    bool do_capture,
+                    bool cancel_active_touches);
 
   // Returns true if the menu host is visible.
   bool IsMenuHostVisible();
 
   // Shows the menu host. If |do_capture| is true the menu host should do a
   // mouse grab.
-  void ShowMenuHost(bool do_capture);
+  void ShowMenuHost(bool do_capture, bool cancel_active_touches);
 
   // Hides the menu host.
   void HideMenuHost();
@@ -67,6 +68,8 @@ class MenuHost : public Widget {
   // Releases a mouse grab installed by |ShowMenuHost|.
   void ReleaseMenuHostCapture();
 
+  void TransferEvents(Widget* source, Widget* target);
+
  private:
   friend class test::MenuControllerTest;
 
@@ -81,6 +84,7 @@ class MenuHost : public Widget {
   // The view we contain.
   SubmenuView* submenu_;
 
+  Widget* owner_ = NULL;
   // If true, DestroyMenuHost has been invoked.
   bool destroying_;