mash: Migrate [Keyboard]Brightness code to ash/common.

ash/test/ash_test_base.cc

Index: ash/test/ash_test_base.cc
diff --git a/ash/test/ash_test_base.cc b/ash/test/ash_test_base.cc
index c6d860953b8f5cef0f6a158067340660b43f6b05..4f713e727450faf33fe480cc9f7372d9b0b72aa8 100644
--- a/ash/test/ash_test_base.cc
+++ b/ash/test/ash_test_base.cc
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "ash/common/ash_switches.h"
+#include "ash/common/system/brightness_control_delegate.h"
 #include "ash/common/wm/window_positioner.h"
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
@@ -359,5 +360,11 @@ void AshTestBase::DisableIME() {
           ->input_method_event_handler());
 }
 
+void AshTestBase::SetBrightnessControlDelegate(
+    std::unique_ptr<BrightnessControlDelegate> brightness_control_delegate) {
+  WmShell::Get()->SetBrightnessControlDelegate(
+      std::move(brightness_control_delegate));
+}
+
 }  // namespace test
 }  // namespace ash