keep only one typedef for the native drawing context

ui/gfx/native_widget_types.h

Index: ui/gfx/native_widget_types.h
diff --git a/ui/gfx/native_widget_types.h b/ui/gfx/native_widget_types.h
index 4e1e2256b31af8734402b8027fb16a2caaecf9a6..640a200fb29109ef9735458b6b5715ed00814d1e 100644
--- a/ui/gfx/native_widget_types.h
+++ b/ui/gfx/native_widget_types.h
@@ -137,11 +137,9 @@ typedef jobject NativeEvent;
 
 #if defined(OS_WIN)
 typedef HFONT NativeFont;
-typedef HDC NativeDrawingContext;
 typedef IAccessible* NativeViewAccessible;
 #elif defined(OS_IOS)
 typedef UIFont* NativeFont;
-typedef CGContext* NativeDrawingContext;
 #ifdef __OBJC__
 typedef id NativeViewAccessible;
 #else
@@ -149,7 +147,6 @@ typedef void* NativeViewAccessible;
 #endif  // __OBJC__
 #elif defined(OS_MACOSX)
 typedef NSFont* NativeFont;
-typedef CGContext* NativeDrawingContext;
 #ifdef __OBJC__
 typedef id NativeViewAccessible;
 #else
@@ -157,11 +154,6 @@ typedef void* NativeViewAccessible;
 #endif  // __OBJC__
 #else  // Android, Linux, Chrome OS, etc.
 // Linux doesn't have a native font type.
-#if defined(USE_CAIRO)
-typedef cairo_t* NativeDrawingContext;
-#else
-typedef void* NativeDrawingContext;
-#endif  // defined(USE_CAIRO)
 #if defined(USE_X11) && !defined(OS_CHROMEOS)
 typedef AtkObject* NativeViewAccessible;
 #else