Add a specialized apps::NativeAppWindow for app_shell

apps/shell/browser/shell_browser_main_parts.cc

Index: apps/shell/browser/shell_browser_main_parts.cc
diff --git a/apps/shell/browser/shell_browser_main_parts.cc b/apps/shell/browser/shell_browser_main_parts.cc
index 090d97f3cd535569686c951a8ce5895deae3015e..3a4ebadadb16f1b34cbd3cda999528ef487d32ab 100644
--- a/apps/shell/browser/shell_browser_main_parts.cc
+++ b/apps/shell/browser/shell_browser_main_parts.cc
@@ -4,6 +4,7 @@
 
 #include "apps/shell/browser/shell_browser_main_parts.h"
 
+#include "apps/shell/browser/shell_apps_client.h"
 #include "apps/shell/browser/shell_browser_context.h"
 #include "apps/shell/browser/shell_extension_system.h"
 #include "apps/shell/browser/shell_extensions_browser_client.h"
@@ -108,6 +109,9 @@ void ShellBrowserMainParts::PreMainMessageLoopRun() {
       new extensions::ShellExtensionsBrowserClient(browser_context_.get()));
   extensions::ExtensionsBrowserClient::Set(extensions_browser_client_.get());
 
+  apps_client_.reset(new ShellAppsClient(browser_context_.get()));
+  AppsClient::Set(apps_client_.get());
+
   // Create our custom ExtensionSystem first because other
   // BrowserContextKeyedServices depend on it.
   CreateExtensionSystem();
@@ -155,6 +159,7 @@ void ShellBrowserMainParts::PostMainMessageLoopRun() {
 
 void ShellBrowserMainParts::OnWindowTreeHostCloseRequested(
     const aura::RootWindow* root) {
+  extension_system_->CloseApp();
   base::MessageLoop::current()->PostTask(FROM_HERE,
                                          base::MessageLoop::QuitClosure());
 }