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

ash/common/wm/forwarding_layer_delegate.cc

+// 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 "ash/common/wm/forwarding_layer_delegate.h"
+
+#include "ash/common/wm_window.h"
+#include "base/callback.h"
+#include "ui/compositor/layer.h"
+
+namespace ash {
+namespace wm {
+
+ForwardingLayerDelegate::ForwardingLayerDelegate(WmWindow* original_window,
+                                                 ui::LayerDelegate* delegate)
+    : original_window_(original_window), original_delegate_(delegate) {}
+
+ForwardingLayerDelegate::~ForwardingLayerDelegate() {}
+
+void ForwardingLayerDelegate::OnPaintLayer(const ui::PaintContext& context) {
+  if (!original_delegate_)
+    return;
+  // |original_delegate_| may have already been deleted or
+  // disconnected by this time. Check if |original_delegate_| is still
+  // used by the original_window tree, or skip otherwise.
+  if (IsDelegateValid(original_window_->GetLayer()))
+    original_delegate_->OnPaintLayer(context);
+  else
+    original_delegate_ = nullptr;
+}
+
+void ForwardingLayerDelegate::OnDelegatedFrameDamage(
+    const gfx::Rect& damage_rect_in_dip) {}
+
+void ForwardingLayerDelegate::OnDeviceScaleFactorChanged(
+    float device_scale_factor) {
+  // Don't tell the original delegate about device scale factor change
+  // on cloned layer because the original layer is still on the same display.
+}
+
+base::Closure ForwardingLayerDelegate::PrepareForLayerBoundsChange() {
+  return base::Closure();
+}
+
+bool ForwardingLayerDelegate::IsDelegateValid(ui::Layer* layer) const {
+  if (layer->delegate() == original_delegate_)
+    return true;
+  for (auto* child : layer->children()) {
+    if (IsDelegateValid(child))
+      return true;
+  }
+  return false;
+}
+
+}  // namespace wm
+}  // namespace ash