Call ShowRootWindow on NativeWindow's RootWindow to display the window.

content/shell/minimal_ash.cc

Index: content/shell/minimal_ash.cc
diff --git a/content/shell/minimal_ash.cc b/content/shell/minimal_ash.cc
index e1ff94abd8d95b426521059c8a7c93b9ae8d9c96..fdecda2ad69ad34b08d3877508eacc4698dc21a2 100644
--- a/content/shell/minimal_ash.cc
+++ b/content/shell/minimal_ash.cc
@@ -13,9 +13,10 @@
 
 namespace content {
 
-MinimalAsh::MinimalAsh() {
+MinimalAsh::MinimalAsh(const gfx::Size& default_window_size) {
   root_window_.reset(new aura::RootWindow(
-      aura::RootWindow::CreateParams(gfx::Rect(100, 100))));
+      aura::RootWindow::CreateParams(
+          gfx::Rect(default_window_size))));
   root_window_->Init();
   aura::client::SetStackingClient(root_window_.get(), this);