platform-window: Add a PlatformWindowFactory for creating windows.

ui/platform_window/win/win_window_factory.cc

+// Copyright 2014 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 "ui/platform_window/win/win_window_factory.h"
+
+#include "ui/platform_window/win/win_window.h"
+
+namespace ui {
+
+WinWindowFactory::WinWindowFactory() {
+}
+
+WinWindowFactory::~WinWindowFactory() {
+}
+
+// static
+PlatformWindowFactory* WinWindowFactory::CreateIfNecessary() {
+  PlatformWindowFactory* instance = GetInstance();
+  if (!instance)
+    new WinWindowFactory();
+  instance = GetInstance();
+  CHECK(instance);
+  return instance;
+}
+
+scoped_ptr<PlatformWindow> WinWindowFactory::CreatePlatformWindow(
+    PlatformWindowDelegate* delegate,
+    const gfx::Rect& bounds) {
+  return scoped_ptr<PlatformWindow>(new WinWindow(delegate, bounds));
+}
+
+}  // namespace ui