[OverlayWindow] Add platform-independent window and views implementation.

chrome/browser/ui/views/overlay/overlay_window_views.h

+// 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 CHROME_BROWSER_UI_VIEWS_OVERLAY_OVERLAY_WINDOW_VIEWS_H_
+#define CHROME_BROWSER_UI_VIEWS_OVERLAY_OVERLAY_WINDOW_VIEWS_H_
+
+#include "chrome/browser/ui/overlay/overlay_window.h"
+#include "ui/views/widget/widget.h"

[sky, 2017/07/18 16:48:07]

Forward declare Widget.

[apacible, 2017/07/19 00:44:12]

Done.

+
+// The Views implementation of OverlayWindow.
+class OverlayWindowViews : public OverlayWindow {
+ public:
+  OverlayWindowViews();
+  ~OverlayWindowViews() override;
+
+  void Init() override;

[sky, 2017/07/18 16:48:07]

Generally we prefix overrides with a comment as to what class the overrides is
from. For example:
// OverlayWindow:

[apacible, 2017/07/19 00:44:12]

Done.

+  bool IsActive() const override;
+  void Show() override;
+  void Hide() override;
+  void Close() override;
+  void Activate() override;
+  bool IsAlwaysOnTop() const override;
+  ui::Layer* GetLayer() override;
+  gfx::NativeWindow GetNativeWindow() const override;
+  gfx::Rect GetBounds() const override;
+
+ private:
+  std::unique_ptr<views::Widget> widget_;

[sky, 2017/07/18 16:48:07]

If you're going to own the widget then you should use WIDGET_OWNS_NATIVE_WIDGET
in the InitParams.

[apacible, 2017/07/19 00:44:12]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(OverlayWindowViews);
+};
+
+#endif  // CHROME_BROWSER_UI_VIEWS_OVERLAY_OVERLAY_WINDOW_VIEWS_H_