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

ui/gfx/platform_font.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_GFX_PLATFORM_FONT_
 #define UI_GFX_PLATFORM_FONT_
 #pragma once
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
 #include "base/string16.h"
 #include "ui/gfx/native_widget_types.h"
+#include "ui/ui_api.h"
 
 namespace gfx {
 
 class Font;
 
-class PlatformFont : public base::RefCounted<PlatformFont> {
+class UI_API PlatformFont : public base::RefCounted<PlatformFont> {
  public:
   // Create an appropriate PlatformFont implementation.
   static PlatformFont* CreateDefault();
   static PlatformFont* CreateFromFont(const Font& other);
   static PlatformFont* CreateFromNativeFont(NativeFont native_font);
   static PlatformFont* CreateFromNameAndSize(const string16& font_name,
                                              int font_size);
 
   // Returns a new Font derived from the existing font.
   // size_delta is the size to add to the current font. See the single
@@ skipping 40 matching lines @@
   virtual ~PlatformFont() {}
 
  private:
   friend class base::RefCounted<PlatformFont>;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_PLATFORM_FONT_