Use helper DeviceChangeHandler to call mousecontrol/tpcontrol whenever a device is attached.

chrome/browser/chromeos/preferences.h

Index: chrome/browser/chromeos/preferences.h
===================================================================
--- chrome/browser/chromeos/preferences.h	(revision 200880)
+++ chrome/browser/chromeos/preferences.h	(working copy)
@@ -11,6 +11,7 @@
 #include "base/compiler_specific.h"
 #include "base/prefs/pref_member.h"
 #include "chrome/browser/chromeos/language_preferences.h"
+#include "chrome/browser/chromeos/system/pointer_device_observer.h"
 #include "chrome/browser/prefs/pref_service_syncable_observer.h"
 
 class PrefRegistrySimple;
@@ -31,7 +32,8 @@
 // is first initialized, it will initialize the OS settings to what's stored in
 // the preferences. These include touchpad settings, etc.
 // When the preferences change, we change the settings to reflect the new value.
-class Preferences : public PrefServiceSyncableObserver {
+class Preferences : public PrefServiceSyncableObserver,
+                    public system::PointerDeviceObserver::Observer {
  public:
   Preferences();
   explicit Preferences(
@@ -103,12 +105,21 @@
   // on the cmd line.
   void ForceNaturalScrollDefault();
 
+  // Helpers for preference changes for mouse and touchpad settings.
+  void SetTouchpadPrefs(const std::string* pref_name);
+  void SetMousePrefs(const std::string* pref_name);
+
   // PrefServiceSyncableObserver implementation.
   virtual void OnIsSyncingChanged() OVERRIDE;
 
+  // PointerDeviceObserver::Observer implementation.
+  virtual void TouchpadExists(bool exists) OVERRIDE;
+  virtual void MouseExists(bool exists) OVERRIDE;
+
   PrefServiceSyncable* prefs_;
 
   input_method::InputMethodManager* input_method_manager_;
+  scoped_ptr<system::PointerDeviceObserver> pointer_device_observer_;
 
   BooleanPrefMember tap_to_click_enabled_;
   BooleanPrefMember tap_dragging_enabled_;