[CrOS] Initial rough cut of alt-tab window cycling UI.

ash/wm/forwarding_layer_delegate.h

Index: ash/wm/forwarding_layer_delegate.h
diff --git a/ash/wm/forwarding_layer_delegate.h b/ash/wm/forwarding_layer_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..71c152209b73ebd78ca4660fdb5abfa71f3d3f83
--- /dev/null
+++ b/ash/wm/forwarding_layer_delegate.h
@@ -0,0 +1,40 @@
+// Copyright 2016 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.
+
+#include "base/macros.h"
+#include "ui/compositor/layer_delegate.h"
+
+namespace ui {
+class Layer;
+}
+
+namespace ash {
+
+class WmWindow;
+
+// A layer delegate to paint the content of the recreated layers by delegating
+// the paint request to the original delegate. It checks if the orignal delegate
+// is still valid by traversing the original layers.
+class ForwardingLayerDelegate : public ui::LayerDelegate {
+ public:
+  ForwardingLayerDelegate(WmWindow* original_window,
+                          ui::LayerDelegate* delegate);
+  ~ForwardingLayerDelegate() override;
+
+ private:
+  // ui:LayerDelegate:
+  void OnPaintLayer(const ui::PaintContext& context) override;
+  void OnDelegatedFrameDamage(const gfx::Rect& damage_rect_in_dip) override;
+  void OnDeviceScaleFactorChanged(float device_scale_factor) override;
+  base::Closure PrepareForLayerBoundsChange() override;
+
+  bool IsDelegateValid(ui::Layer* layer);
+
+  WmWindow* original_window_;
+  ui::LayerDelegate* original_delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(ForwardingLayerDelegate);
+};
+
+}  // namespace ash