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

services/ui/public/cpp/window_observer.h

Index: services/ui/public/cpp/window_observer.h
diff --git a/services/ui/public/cpp/window_observer.h b/services/ui/public/cpp/window_observer.h
index 8d54835372cbbda83409ff9edad999185af487ef..1858ebb6290b9a9ac9bfde48f4ad04c9b5f72fa6 100644
--- a/services/ui/public/cpp/window_observer.h
+++ b/services/ui/public/cpp/window_observer.h
@@ -9,6 +9,7 @@
 
 #include <vector>
 
+#include "services/ui/public/cpp/ui_export.h"
 #include "services/ui/public/cpp/window.h"
 
 namespace ui {
@@ -25,9 +26,9 @@ class Window;
 // prior to being called, so for example in the case of OnWindowDestroying(),
 // it's possible the window has already been destroyed on the service side.
 
-class WindowObserver {
+class UI_EXPORT WindowObserver {
  public:
-  struct TreeChangeParams {
+  struct UI_EXPORT TreeChangeParams {
     TreeChangeParams();
     Window* target;
     Window* old_parent;