ash/mash: Add a mus-client that sets up ash to provide the system ui for mash.

mash/shell/shell_application_delegate.cc

Index: mash/shell/shell_application_delegate.cc
diff --git a/mash/shell/shell_application_delegate.cc b/mash/shell/shell_application_delegate.cc
index 1cb6e27a63da5102d83932e2d21a5001a1178794..5b5a1cdb7da5f7c497978f3103c6d625b46fa9ee 100644
--- a/mash/shell/shell_application_delegate.cc
+++ b/mash/shell/shell_application_delegate.cc
@@ -5,9 +5,16 @@
 #include "mash/shell/shell_application_delegate.h"
 
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "mojo/shell/public/cpp/application_connection.h"
 #include "mojo/shell/public/cpp/application_impl.h"
 
+namespace {
+
+const char kUseAshSysui[] = "use-ash-sysui";
+
+}  // namespace
+
 namespace mash {
 namespace shell {
 
@@ -20,8 +27,7 @@ void ShellApplicationDelegate::Initialize(mojo::ApplicationImpl* app) {
   app_ = app;
   StartBrowserDriver();
   StartWindowManager();
-  StartWallpaper();
-  StartShelf();
+  StartSystemUI();
   StartQuickLaunch();
 }
 
@@ -71,6 +77,19 @@ void ShellApplicationDelegate::StartWindowManager() {
                  base::Unretained(this)));
 }
 
+void ShellApplicationDelegate::StartSystemUI() {
+  static bool use_ash =
+      base::CommandLine::ForCurrentProcess()->HasSwitch(kUseAshSysui);
+  if (use_ash) {
+    StartRestartableService("mojo:ash_sysui",
+                            base::Bind(&ShellApplicationDelegate::StartSystemUI,
+                                       base::Unretained(this)));
+  } else {
+    StartWallpaper();
+    StartShelf();
+  }
+}
+
 void ShellApplicationDelegate::StartWallpaper() {
   StartRestartableService("mojo:wallpaper",
                           base::Bind(&ShellApplicationDelegate::StartWallpaper,