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

ui/base/dragdrop/drop_target.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_DRAGDROP_DROP_TARGET_H_
 #define UI_BASE_DRAGDROP_DROP_TARGET_H_
 #pragma once
 
 #include <objidl.h>
 
 #include "base/memory/ref_counted.h"
+#include "ui/ui_api.h"
 
 // Windows interface.
 struct IDropTargetHelper;
 
 namespace ui {
 
 // A DropTarget implementation that takes care of the nitty gritty
 // of dnd. While this class is concrete, subclasses will most likely
 // want to override various OnXXX methods.
 //
 // Because DropTarget is ref counted you shouldn't delete it directly,
 // rather wrap it in a scoped_refptr. Be sure and invoke RevokeDragDrop(m_hWnd)
 // before the HWND is deleted too.
 //
 // This class is meant to be used in a STA and is not multithread-safe.
-class DropTarget : public IDropTarget {
+class UI_API DropTarget : public IDropTarget {
  public:
   // Create a new DropTarget associating it with the given HWND.
   explicit DropTarget(HWND hwnd);
   virtual ~DropTarget();
 
   // When suspended is set to |true|, the drop target does not receive drops
   // from drags initiated within the owning HWND.
   bool suspended() const { return suspended_; }
   void set_suspended(bool suspended) { suspended_ = suspended; }
 
@@ skipping 76 matching lines @@
   bool suspended_;
 
   LONG ref_count_;
 
   DISALLOW_COPY_AND_ASSIGN(DropTarget);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DRAGDROP_DROP_TARGET_H_