mash: Make the power button shut the system down.

ash/mus/accelerators/accelerator_controller_unittest.cc

Index: ash/mus/accelerators/accelerator_controller_unittest.cc
diff --git a/ash/mus/accelerators/accelerator_controller_unittest.cc b/ash/mus/accelerators/accelerator_controller_unittest.cc
index 0846c34fad55a2d2ab5c4ea9d7706df70222bfb0..a071772d20d15c89d8ebf68afd434e3c7eb8cc76 100644
--- a/ash/mus/accelerators/accelerator_controller_unittest.cc
+++ b/ash/mus/accelerators/accelerator_controller_unittest.cc
@@ -972,10 +972,8 @@ TEST_F(AcceleratorControllerTest, GlobalAccelerators) {
       ui::Accelerator(ui::VKEY_M, ui::EF_SHIFT_DOWN | ui::EF_ALT_DOWN)));
 
   // Lock screen
-  // NOTE: Accelerators that do not work on the lock screen need to be
-  // tested before the sequence below is invoked because it causes a side
-  // effect of locking the screen.
-  EXPECT_TRUE(
+  // TODO(derat): Reenable this once user sessions work in mash.
+  EXPECT_FALSE(
       ProcessInController(ui::Accelerator(ui::VKEY_L, ui::EF_COMMAND_DOWN)));
 #endif
 }