Attempt 2 at:...

app/gfx/native_widget_types.h

 // Copyright (c) 2009 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 APP_GFX_NATIVE_WIDGET_TYPES_H_
 #define APP_GFX_NATIVE_WIDGET_TYPES_H_
 
 #include "base/basictypes.h"
 #include "build/build_config.h"
 
@@ skipping 33 matching lines @@
 #else
 class NSView;
 class NSWindow;
 class NSTextField;
 #endif  // __OBJC__
 #elif defined(USE_X11)
 typedef struct _GdkCursor GdkCursor;
 typedef struct _GtkWidget GtkWidget;
 typedef struct _GtkWindow GtkWindow;
 typedef struct _cairo cairo_t;
+typedef struct _GdkRegion GdkRegion;
 #endif
 
 namespace gfx {
 
 #if defined(OS_WIN)
 typedef HWND NativeView;
 typedef HWND NativeWindow;
 typedef HWND NativeEditView;
 typedef HDC NativeDrawingContext;
 typedef HCURSOR NativeCursor;
 typedef HMENU NativeMenu;
+typedef HRGN NativeRegion;
 #elif defined(OS_MACOSX)
 typedef NSView* NativeView;
 typedef NSWindow* NativeWindow;
 typedef NSTextField* NativeEditView;
 typedef CGContext* NativeDrawingContext;
 typedef void* NativeCursor;
 typedef void* NativeMenu;
 #elif defined(USE_X11)
 typedef GtkWidget* NativeView;
 typedef GtkWindow* NativeWindow;
 typedef GtkWidget* NativeEditView;
 typedef cairo_t* NativeDrawingContext;
 typedef GdkCursor* NativeCursor;
 typedef GtkWidget* NativeMenu;
+typedef GdkRegion* NativeRegion;
 #endif
 
 // Note: for test_shell we're packing a pointer into the NativeViewId. So, if
 // you make it a type which is smaller than a pointer, you have to fix
 // test_shell.
 //
 // See comment at the top of the file for usage.
 typedef intptr_t NativeViewId;
 
 // Convert a NativeViewId to a NativeView.
@@ skipping 48 matching lines @@
   // On OS X we don't have windowed plugins.
   // We use a NULL/0 PluginWindowHandle in shared code to indicate there
   // is no window present, so mirror that behavior here.
   typedef bool PluginWindowHandle;
   const PluginWindowHandle kNullPluginWindow = false;
 #endif
 
 }  // namespace gfx
 
 #endif  // APP_GFX_NATIVE_WIDGET_TYPES_H_