Remove all blimp engine code

blimp/engine/app/ui/blimp_window_tree_host.h

-// Copyright 2015 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 BLIMP_ENGINE_APP_UI_BLIMP_WINDOW_TREE_HOST_H_
-#define BLIMP_ENGINE_APP_UI_BLIMP_WINDOW_TREE_HOST_H_
-
-#include <memory>
-
-#include "base/macros.h"
-#include "ui/aura/window_tree_host_platform.h"
-
-namespace blimp {
-namespace engine {
-
-// This WindowTreeHost represents a top-level window in a blimp client, and its
-// children.
-// Note that the Aura WindowTreeHost impl creates a compositor internally,
-// which will eventually get replaced with client-side rendering.
-class BlimpWindowTreeHost : public aura::WindowTreeHostPlatform {
- public:
-  BlimpWindowTreeHost();
-  ~BlimpWindowTreeHost() override;
-
- private:
-  // aura::WindowTreeHostPlatform overrides.
-  void OnAcceleratedWidgetAvailable(gfx::AcceleratedWidget widget,
-                                    float device_pixel_ratio) override;
-
-  DISALLOW_COPY_AND_ASSIGN(BlimpWindowTreeHost);
-};
-
-}  // namespace engine
-}  // namespace blimp
-
-#endif  // BLIMP_ENGINE_APP_UI_BLIMP_WINDOW_TREE_HOST_H_