Adds a factory function to ViewsDelegate for DesktopWindowTreeHost

ui/views/views_delegate.h

Index: ui/views/views_delegate.h
diff --git a/ui/views/views_delegate.h b/ui/views/views_delegate.h
index 6a784af5fabab6edee098c241b1e1f4e09ff8352..04324b50a4edba52b08125bd4bd80a32b436a015 100644
--- a/ui/views/views_delegate.h
+++ b/ui/views/views_delegate.h
@@ -5,6 +5,7 @@
 #ifndef UI_VIEWS_VIEWS_DELEGATE_H_
 #define UI_VIEWS_VIEWS_DELEGATE_H_
 
+#include <memory>
 #include <string>
 
 #if defined(OS_WIN)
@@ -51,6 +52,8 @@ class View;
 class Widget;
 
 #if defined(USE_AURA)
+class DesktopNativeWidgetAura;
+class DesktopWindowTreeHost;
 class TouchSelectionMenuRunnerViews;
 #endif
 
@@ -98,6 +101,14 @@ class VIEWS_EXPORT ViewsDelegate {
   using NativeWidgetFactory =
       base::Callback<NativeWidget*(const Widget::InitParams&,
                                    internal::NativeWidgetDelegate*)>;
+#if defined(USE_AURA)
+  using DesktopWindowTreeHostFactory =
+      base::Callback<std::unique_ptr<DesktopWindowTreeHost>(
+          const Widget::InitParams&,
+          internal::NativeWidgetDelegate*,
+          DesktopNativeWidgetAura*)>;
+#endif
+
 #if defined(OS_WIN)
   enum AppbarAutohideEdge {
     EDGE_TOP    = 1 << 0,
@@ -124,13 +135,22 @@ class VIEWS_EXPORT ViewsDelegate {
 
   // Call this method to set a factory callback that will be used to construct
   // NativeWidget implementations overriding the platform defaults.
-  void set_native_widget_factory(NativeWidgetFactory factory) {
+  void set_native_widget_factory(const NativeWidgetFactory& factory) {
     native_widget_factory_ = factory;
   }
-  const NativeWidgetFactory& native_widget_factory() {
+  const NativeWidgetFactory& native_widget_factory() const {
     return native_widget_factory_;
   }
 
+#if defined(USE_AURA)
+  void set_desktop_window_tree_host_factory(
+      const DesktopWindowTreeHostFactory& factory) {
+    desktop_window_tree_host_factory_ = factory;
+  }
+  const DesktopWindowTreeHostFactory& desktop_window_tree_host_factory() const {
+    return desktop_window_tree_host_factory_;
+  }
+#endif
   // Saves the position, size and "show" state for the window with the
   // specified name.
   virtual void SaveWindowPlacement(const Widget* widget,
@@ -240,6 +260,8 @@ class VIEWS_EXPORT ViewsDelegate {
 
 #if defined(USE_AURA)
   std::unique_ptr<TouchSelectionMenuRunnerViews> touch_selection_menu_runner_;
+
+  DesktopWindowTreeHostFactory desktop_window_tree_host_factory_;
 #endif
 
   NativeWidgetFactory native_widget_factory_;