mus: Use TooltipManagerAura in NativeWidgetMus.

ui/views/widget/tooltip_manager_aura.h

Index: ui/views/widget/tooltip_manager_aura.h
diff --git a/ui/views/widget/tooltip_manager_aura.h b/ui/views/widget/tooltip_manager_aura.h
index f429385525ab350028c4b4c2ad593b31bac348f6..6de6187b030905b74036ca2549d2519a6ebc2182 100644
--- a/ui/views/widget/tooltip_manager_aura.h
+++ b/ui/views/widget/tooltip_manager_aura.h
@@ -9,6 +9,7 @@
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "ui/gfx/geometry/point.h"
+#include "ui/views/views_export.h"
 #include "ui/views/widget/tooltip_manager.h"
 
 namespace aura {
@@ -24,7 +25,7 @@ namespace views {
 class Widget;
 
 // TooltipManager implementation for Aura.
-class TooltipManagerAura : public TooltipManager {
+class VIEWS_EXPORT TooltipManagerAura : public TooltipManager {
  public:
   explicit TooltipManagerAura(Widget* widget);
   ~TooltipManagerAura() override;