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

ui/gfx/gfx_paths.h

Index: ui/gfx/gfx_paths.h
===================================================================
--- ui/gfx/gfx_paths.h	(revision 92815)
+++ ui/gfx/gfx_paths.h	(working copy)
@@ -6,6 +6,8 @@
 #define UI_GFX_GFX_PATHS_H_
 #pragma once
 
+#include "ui/ui_api.h"
+
 // This file declares path keys for the app module.  These can be used with
 // the PathService to access various special directories and files.
 
@@ -21,7 +23,7 @@
 };
 
 // Call once to register the provider for the path keys defined above.
-void RegisterPathProvider();
+UI_API void RegisterPathProvider();
 
 }  // namespace gfx