mash: Make the power button shut the system down.

ash/mus/bridge/wm_shell_mus.cc

Index: ash/mus/bridge/wm_shell_mus.cc
diff --git a/ash/mus/bridge/wm_shell_mus.cc b/ash/mus/bridge/wm_shell_mus.cc
index ca58c14203786330215a5d4f1997ae352226815f..9658acd3626bfa469545cc73ecd0b9108cd9bf3f 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -32,6 +32,7 @@
 #include "ash/shared/immersive_fullscreen_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_init_params.h"
+#include "ash/wm/lock_state_controller.h"
 #include "ash/wm/window_util.h"
 #include "base/memory/ptr_util.h"
 #include "components/user_manager/user_info_impl.h"
@@ -63,7 +64,11 @@ class SessionStateDelegateStub : public SessionStateDelegate {
   int GetMaximumNumberOfLoggedInUsers() const override { return 3; }
   int NumberOfLoggedInUsers() const override { return 1; }
   bool IsActiveUserSessionStarted() const override { return true; }
-  bool CanLockScreen() const override { return true; }
+  bool CanLockScreen() const override {
+    // The Chrome OS session_manager process currently rejects screen-lock
+    // requests due to no user being logged in.
+    return false;
+  }
   bool IsScreenLocked() const override { return screen_locked_; }
   bool ShouldLockScreenAutomatically() const override { return false; }
   void LockScreen() override {
@@ -390,7 +395,7 @@ void WmShellMus::RemovePointerWatcher(views::PointerWatcher* watcher) {
 }
 
 void WmShellMus::RequestShutdown() {
-  NOTIMPLEMENTED();
+  Shell::GetInstance()->lock_state_controller()->RequestShutdown();
 }
 
 bool WmShellMus::IsTouchDown() {