Add unit tests for screen capture and share notification UI.

ash/system/chromeos/screen_security/screen_share_tray_item.h

Index: ash/system/chromeos/screen_security/screen_share_tray_item.h
diff --git a/ash/system/chromeos/screen_security/screen_share_tray_item.h b/ash/system/chromeos/screen_security/screen_share_tray_item.h
index 84a29d03f9109a73191d4ee0b77787801ae5304d..4624ac2ee69a94cbc7b7805314db872414d78ec5 100644
--- a/ash/system/chromeos/screen_security/screen_share_tray_item.h
+++ b/ash/system/chromeos/screen_security/screen_share_tray_item.h
@@ -15,8 +15,8 @@ class View;
 namespace ash {
 namespace internal {
 
-class ScreenShareTrayItem : public ScreenTrayItem,
-                            public ScreenShareObserver {
+class ASH_EXPORT ScreenShareTrayItem : public ScreenTrayItem,
+                                       public ScreenShareObserver {
  public:
   explicit ScreenShareTrayItem(SystemTray* system_tray);
   virtual ~ScreenShareTrayItem();