Remove views::SingleSplitView as it's presently unused.

ui/views/examples/double_split_view_example.h

Index: ui/views/examples/double_split_view_example.h
diff --git a/ui/views/examples/double_split_view_example.h b/ui/views/examples/double_split_view_example.h
deleted file mode 100644
index 231ddc67adca1063273bdac48aab08b331064919..0000000000000000000000000000000000000000
--- a/ui/views/examples/double_split_view_example.h
+++ /dev/null
@@ -1,35 +0,0 @@
-// Copyright (c) 2011 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_VIEWS_EXAMPLES_DOUBLE_SPLIT_VIEW_EXAMPLE_H_
-#define UI_VIEWS_EXAMPLES_DOUBLE_SPLIT_VIEW_EXAMPLE_H_
-
-#include "base/macros.h"
-#include "ui/views/examples/example_base.h"
-
-namespace views {
-class SingleSplitView;
-
-namespace examples {
-
-class VIEWS_EXAMPLES_EXPORT DoubleSplitViewExample : public ExampleBase {
- public:
-  DoubleSplitViewExample();
-  ~DoubleSplitViewExample() override;
-
-  // ExampleBase:
-  void CreateExampleView(View* container) override;
-
- private:
-  // The SingleSplitViews to be embedded.
-  SingleSplitView* outer_single_split_view_;
-  SingleSplitView* inner_single_split_view_;
-
-  DISALLOW_COPY_AND_ASSIGN(DoubleSplitViewExample);
-};
-
-}  // namespace examples
-}  // namespace views
-
-#endif  // UI_VIEWS_EXAMPLES_DOUBLE_SPLIT_VIEW_EXAMPLE_H_