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..7132da07f9624fa4ed41c23d15ea05e9bff8df48 100644
--- a/ui/views/controls/menu/menu_host.h
+++ b/ui/views/controls/menu/menu_host.h
@@ -10,6 +10,7 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/gfx/geometry/rect.h"
+#include "ui/views/controls/menu/menu_controller.h"
 #include "ui/views/widget/widget.h"
 
 namespace views {
@@ -78,6 +79,14 @@ class MenuHost : public Widget {
   void OnDragWillStart() override;
   void OnDragComplete() override;
 
+#if defined(OS_CHROMEOS)
+  // Current active MenuController instance.
+  MenuController* controller = MenuController::GetActiveInstance();

[xiyuan, 2017/05/16 22:46:57]

This is not needed and should not be done here.

We can get MenuController via
 submenu_->GetMenuItem()->GetMenuController()

as in MenuHost::InitMenuHost [1]

[1]:
https://cs.chromium.org/chromium/src/ui/views/controls/menu/menu_host.cc?rcl=...

[minch1, 2017/05/17 16:55:38]

Done.

+
+  // The owner of child windows.

[xiyuan, 2017/05/16 22:46:57]

This not exactly correct. It is "parent of the MenuHost widget".

[minch1, 2017/05/17 16:55:38]

Done.

+  Widget* owner_ = nullptr;
+#endif
+
   // The view we contain.
   SubmenuView* submenu_;