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..85c141f45831ee949d5e70eab0d4f2d31a13d593 100644
--- a/ui/views/controls/menu/menu_host.h
+++ b/ui/views/controls/menu/menu_host.h
@@ -67,6 +67,8 @@ class MenuHost : public Widget {
   // Releases a mouse grab installed by |ShowMenuHost|.
   void ReleaseMenuHostCapture();
 
+  void TransferEvents(Widget* source, Widget* target);

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

This does not depend on any MenuHost state and not called externally. So let's
put it in an anonymous namespace in cc file. Also maybe call it TransferGesture
to be more accurate.

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

Done.

+
  private:
   friend class test::MenuControllerTest;
 
@@ -81,6 +83,7 @@ class MenuHost : public Widget {
   // The view we contain.
   SubmenuView* submenu_;
 
+  Widget* owner_ = NULL;

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

Document the member and insert an empty line after it.

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

NULL -> nullptr

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

Done.

   // If true, DestroyMenuHost has been invoked.
   bool destroying_;