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

ui/gfx/gtk_native_view_id_manager.h

Index: ui/gfx/gtk_native_view_id_manager.h
===================================================================
--- ui/gfx/gtk_native_view_id_manager.h	(revision 92815)
+++ ui/gfx/gtk_native_view_id_manager.h	(working copy)
@@ -11,6 +11,7 @@
 #include "base/memory/singleton.h"
 #include "base/synchronization/lock.h"
 #include "ui/gfx/native_widget_types.h"
+#include "ui/ui_api.h"
 
 typedef unsigned long XID;
 struct _GtkPreserveWindow;
@@ -30,7 +31,7 @@
 // pointers and observes the various signals from the widget for when an X
 // window is created, destroyed etc. Thus it provides a thread safe mapping
 // from NativeViewIds to the current XID for that widget.
-class GtkNativeViewManager {
+class UI_API GtkNativeViewManager {
  public:
   // Returns the singleton instance.
   static GtkNativeViewManager* GetInstance();