Introduce ui.dll / libui.so for the component build.

ui/base/x/active_window_watcher_x.h

Index: ui/base/x/active_window_watcher_x.h
===================================================================
--- ui/base/x/active_window_watcher_x.h	(revision 92815)
+++ ui/base/x/active_window_watcher_x.h	(working copy)
@@ -12,13 +12,14 @@
 #include "base/memory/singleton.h"
 #include "base/observer_list.h"
 #include "ui/base/gtk/gtk_signal.h"
+#include "ui/ui_api.h"
 
 namespace ui {
 
 // This is a helper class that is used to keep track of which window the X
 // window manager thinks is active. Add an Observer to listener for changes to
 // the active window.
-class ActiveWindowWatcherX {
+class UI_API ActiveWindowWatcherX {
  public:
   class Observer {
    public: