services/ui: Create a proper component for the client-lib.

services/ui/public/cpp/lib/window_private.h

Index: services/ui/public/cpp/lib/window_private.h
diff --git a/services/ui/public/cpp/lib/window_private.h b/services/ui/public/cpp/lib/window_private.h
index b30c75d9cf38a037bdf1284f92a8be2cdf821f4b..e005a7a8199f8031da36994a57c5f48aef6122ce 100644
--- a/services/ui/public/cpp/lib/window_private.h
+++ b/services/ui/public/cpp/lib/window_private.h
@@ -11,13 +11,14 @@
 
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/array.h"
+#include "services/ui/public/cpp/ui_export.h"
 #include "services/ui/public/cpp/window.h"
 
 namespace ui {
 
 // This class is a friend of a Window and contains functions to mutate internal
 // state of Window.
-class WindowPrivate {
+class UI_EXPORT WindowPrivate {
  public:
   explicit WindowPrivate(Window* window);
   ~WindowPrivate();