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

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

+// 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.
+
+#include "chrome/browser/ui/views/overlay/overlay_window_views.h"
+
+// static
+std::unique_ptr<OverlayWindow> OverlayWindow::Create() {
+  return base::WrapUnique(new OverlayWindowViews());
+}
+
+OverlayWindowViews::OverlayWindowViews() {
+  widget_.reset(new views::Widget());
+}
+
+OverlayWindowViews::~OverlayWindowViews() = default;
+
+void OverlayWindowViews::Init() {
+  // TODO(apacible): Finalize the type of widget.
+  views::Widget::InitParams params(views::Widget::InitParams::TYPE_WINDOW);
+
+  // TODO(apacible): Update preferred sizing and positioning.
+  params.bounds = gfx::Rect(200, 200, 700, 500);
+  params.keep_on_top = true;
+  params.visible_on_all_workspaces = true;
+
+  widget_->Init(params);
+  widget_->Show();
+
+  // TODO(apacible): Set the WidgetDelegate for more control over behavior.

[mlamouri (slow - plz ping), 2017/07/07 10:34:38]

could you have this TODO and the above point to the bug number?

[apacible, 2017/07/18 01:08:28]

Done.

+}
+
+bool OverlayWindowViews::IsActive() const {
+  return widget_->IsActive();
+}
+
+void OverlayWindowViews::Show() {
+  widget_->Show();
+}
+
+void OverlayWindowViews::Hide() {
+  widget_->Hide();
+}
+
+void OverlayWindowViews::Close() {
+  widget_->Close();
+}
+
+void OverlayWindowViews::Activate() {
+  widget_->Activate();
+}
+
+bool OverlayWindowViews::IsAlwaysOnTop() const {
+  return true;
+}
+
+ui::Layer* OverlayWindowViews::GetLayer() {
+  return widget_->GetLayer();
+}
+
+gfx::NativeWindow OverlayWindowViews::GetNativeWindow() const {
+  return widget_->GetNativeWindow();
+}
+
+// Retrieves the window's current bounds, including its window.

[mlamouri (slow - plz ping), 2017/07/07 10:34:38]

Is this comment needed?

[sky, 2017/07/11 18:02:25]

This comment should be in overlay_window.h

+gfx::Rect OverlayWindowViews::GetBounds() const {
+  return widget_->GetRestoredBounds();
+}