chromeos: makes it possible for windows to outlive WindowTreeClient

ui/aura/window_port_for_shutdown.h

Index: ui/aura/window_port_for_shutdown.h
diff --git a/ui/aura/window_port_for_shutdown.h b/ui/aura/window_port_for_shutdown.h
new file mode 100644
index 0000000000000000000000000000000000000000..894e2c7259f74b830da181b31bd3515cd10a1863
--- /dev/null
+++ b/ui/aura/window_port_for_shutdown.h
@@ -0,0 +1,47 @@
+// Copyright 2017 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_AURA_WINDOW_PORT_FOR_SHUTDOWN_H_
+#define UI_AURA_WINDOW_PORT_FOR_SHUTDOWN_H_
+
+#include "ui/aura/window_port.h"
+
+namespace aura {
+
+// When WindowTreeClient is destroyed any existing windows get a
+// WindowPortForShutdown assigned to them. This allows for the Window to keep
+// working without a WindowTreeClient. This class is *only* used inside aura.
+class WindowPortForShutdown : public WindowPort {
+ public:
+  WindowPortForShutdown();
+  ~WindowPortForShutdown() override;
+
+  static void Install(aura::Window* window);
+
+  // WindowPort:
+  void OnPreInit(Window* window) override;
+  void OnDeviceScaleFactorChanged(float device_scale_factor) override;
+  void OnWillAddChild(Window* child) override;
+  void OnWillRemoveChild(Window* child) override;
+  void OnWillMoveChild(size_t current_index, size_t dest_index) override;
+  void OnVisibilityChanged(bool visible) override;
+  void OnDidChangeBounds(const gfx::Rect& old_bounds,
+                         const gfx::Rect& new_bounds) override;
+  std::unique_ptr<ui::PropertyData> OnWillChangeProperty(
+      const void* key) override;
+  void OnPropertyChanged(const void* key,
+                         int64_t old_value,
+                         std::unique_ptr<ui::PropertyData> data) override;
+  std::unique_ptr<cc::CompositorFrameSink> CreateCompositorFrameSink() override;
+  cc::SurfaceId GetSurfaceId() const override;
+  void OnWindowAddedToRootWindow() override;
+  void OnWillRemoveWindowFromRootWindow() override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(WindowPortForShutdown);
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_WINDOW_PORT_FOR_SHUTDOWN_H_