Introduce mash/shell

mash/system_ui/main.cc

Index: mash/system_ui/main.cc
diff --git a/mash/example/mock_sysui/main.cc b/mash/system_ui/main.cc
similarity index 77%
rename from mash/example/mock_sysui/main.cc
rename to mash/system_ui/main.cc
index 44d00e93fe5db459d11ee86daea429b9f911e07a..d36c2e05d3c819ab0d44a2db285a07ded88359b0 100644
--- a/mash/example/mock_sysui/main.cc
+++ b/mash/system_ui/main.cc
@@ -2,11 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "mash/example/mock_sysui/mock_sysui.h"
+#include "mash/system_ui/system_ui.h"
 #include "mojo/application/public/cpp/application_runner.h"
 #include "mojo/public/c/system/main.h"
 
 MojoResult MojoMain(MojoHandle shell_handle) {
-  mojo::ApplicationRunner runner(new MockSysUI);
+  mojo::ApplicationRunner runner(new mash::system_ui::SystemUI);
   return runner.Run(shell_handle);
 }