MD Settings: Update some Settings handlers to use new JS lifecycle management.

chrome/browser/ui/webui/settings/chromeos/device_keyboard_handler.h

Index: chrome/browser/ui/webui/settings/chromeos/device_keyboard_handler.h
diff --git a/chrome/browser/ui/webui/settings/chromeos/device_keyboard_handler.h b/chrome/browser/ui/webui/settings/chromeos/device_keyboard_handler.h
index 55d02ac0a72fc1bcdb5a686c3469535b2122f4bc..15abad65e83ef8a2a30875c145fcf6c298a65153 100644
--- a/chrome/browser/ui/webui/settings/chromeos/device_keyboard_handler.h
+++ b/chrome/browser/ui/webui/settings/chromeos/device_keyboard_handler.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_CHROMEOS_DEVICE_KEYBOARD_HANDLER_H_
 
 #include "base/macros.h"
+#include "base/scoped_observer.h"
 #include "chrome/browser/ui/webui/settings/settings_page_ui_handler.h"
 #include "ui/events/devices/input_device_event_observer.h"
 
@@ -17,6 +18,10 @@ namespace content {
 class WebUI;
 }
 
+namespace ui {
+class DeviceDataManager;
+}
+
 class Profile;
 
 namespace chromeos {
@@ -32,6 +37,8 @@ class KeyboardHandler
 
   // SettingsPageUIHandler implementation.
   void RegisterMessages() override;
+  void OnJavascriptAllowed() override;
+  void OnJavascriptDisallowed() override;
 
   // ui::InputDeviceEventObserver implementation.
   void OnKeyboardDeviceConfigurationChanged() override;
@@ -45,10 +52,12 @@ class KeyboardHandler
 
   // Shows or hides the Caps Lock and Diamond key settings based on whether the
   // system status.
-  void UpdateShowKeys() const;
+  void UpdateShowKeys();
 
   Profile* profile_;  // Weak pointer.
 
+  ScopedObserver<ui::DeviceDataManager, KeyboardHandler> observer_;
+
   DISALLOW_COPY_AND_ASSIGN(KeyboardHandler);
 };