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

ash/common/wm_shell.cc

Index: ash/common/wm_shell.cc
diff --git a/ash/common/wm_shell.cc b/ash/common/wm_shell.cc
index 85613582b8f8acc9d42b5304f93918303b6f013a..6aebb2d7d0aa4177cbd78d475fbd554b254d1477 100644
--- a/ash/common/wm_shell.cc
+++ b/ash/common/wm_shell.cc
@@ -8,6 +8,7 @@
 #include "ash/common/keyboard/keyboard_ui.h"
 #include "ash/common/shell_delegate.h"
 #include "ash/common/shell_window_ids.h"
+#include "ash/common/system/brightness_control_delegate.h"
 #include "ash/common/system/chromeos/session/logout_confirmation_controller.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "ash/common/system/tray/system_tray_notifier.h"
@@ -82,6 +83,11 @@ bool WmShell::IsSystemModalWindowOpen() {
   return false;
 }
 
+void WmShell::SetBrightnessControlDelegate(
+    std::unique_ptr<BrightnessControlDelegate> brightness_control_delegate) {
+  brightness_control_delegate_ = std::move(brightness_control_delegate);
+}
+
 void WmShell::SetKeyboardUI(std::unique_ptr<KeyboardUI> keyboard_ui) {
   keyboard_ui_ = std::move(keyboard_ui);
 }