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

ui/base/dragdrop/drag_source.h

Index: ui/base/dragdrop/drag_source.h
===================================================================
--- ui/base/dragdrop/drag_source.h	(revision 92815)
+++ ui/base/dragdrop/drag_source.h	(working copy)
@@ -10,6 +10,7 @@
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
+#include "ui/ui_api.h"
 
 namespace ui {
 
@@ -17,8 +18,8 @@
 // drag-drop operation as the user mouses over other drop targets on their
 // system. This object tells Windows whether or not the drag should continue,
 // and supplies the appropriate cursors.
-class DragSource : public IDropSource,
-                   public base::RefCountedThreadSafe<DragSource> {
+class UI_API DragSource : public IDropSource,
+                          public base::RefCountedThreadSafe<DragSource> {
  public:
   DragSource();
   virtual ~DragSource() {}