Add context to gfx::Screen calls in support of simultaneous desktop+ash

ui/gfx/screen_type_delegate.h

Index: ui/gfx/screen_type_delegate.h
diff --git a/ui/gfx/screen_type_delegate.h b/ui/gfx/screen_type_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..708ddd53038abac07e7980d44ae2945f1046cc83
--- /dev/null
+++ b/ui/gfx/screen_type_delegate.h
@@ -0,0 +1,28 @@
+// Copyright 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_SCREEN_TYPE_DELEGATE_H_
+#define UI_GFX_SCREEN_TYPE_DELEGATE_H_
+
+#include "ui/gfx/native_widget_types.h"
+
+namespace gfx {
+
+enum UI_EXPORT ScreenType {
+  SCREEN_TYPE_NATIVE = 0,
+  SCREEN_TYPE_ALTERNATE,
+  SCREEN_TYPE_LAST = SCREEN_TYPE_ALTERNATE,
+};
+
+class UI_EXPORT ScreenTypeDelegate {
+ public:
+  virtual ~ScreenTypeDelegate() {}
+
+  // Determines which ScreenType a given |view| belongs to.
+  virtual ScreenType GetScreenTypeForNativeView(NativeView view) = 0;
+};
+
+}  // namespace gfx
+
+#endif  // UI_GFX_SCREEN_TYPE_DELEGATE_H_