Revert of Revert of views: Move TOOLKIT_VIEWS definition in //ui/views/ from root.

ui/gfx/native_widget_types.h

 // Copyright (c) 2012 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_NATIVE_WIDGET_TYPES_H_
 #define UI_GFX_NATIVE_WIDGET_TYPES_H_
 
 #include "build/build_config.h"
 
 #if defined(OS_ANDROID)
@@ skipping 117 matching lines @@
 #elif defined(OS_MACOSX)
 typedef NSCursor* NativeCursor;
 typedef NSView* NativeView;
 typedef NSWindow* NativeWindow;
 typedef NSEvent* NativeEvent;
 #elif defined(OS_ANDROID)
 typedef void* NativeCursor;
 typedef ui::ViewAndroid* NativeView;
 typedef ui::WindowAndroid* NativeWindow;
 typedef jobject NativeEvent;
+#else
+#error Unknown build environment.
 #endif
 
 #if defined(OS_WIN)
 typedef HFONT NativeFont;
 typedef HWND NativeEditView;
 typedef HDC NativeDrawingContext;
 typedef IAccessible* NativeViewAccessible;
 #elif defined(OS_IOS)
 typedef UIFont* NativeFont;
 typedef UITextField* NativeEditView;
@@ skipping 121 matching lines @@
 #elif defined(USE_OZONE)
 typedef intptr_t AcceleratedWidget;
 const AcceleratedWidget kNullAcceleratedWidget = 0;
 #else
 #error unknown platform
 #endif
 
 }  // namespace gfx
 
 #endif  // UI_GFX_NATIVE_WIDGET_TYPES_H_