Reverting this CL because it was committed before I gave the final LGTM.

chrome/browser/chromeos/preferences.cc

Index: chrome/browser/chromeos/preferences.cc
===================================================================
--- chrome/browser/chromeos/preferences.cc	(revision 162209)
+++ chrome/browser/chromeos/preferences.cc	(working copy)
@@ -97,12 +97,16 @@
                                false,
                                PrefService::UNSYNCABLE_PREF);
   }
-  prefs->RegisterBooleanPref(prefs::kScreenMagnifierEnabled,
-                             false,
-                             PrefService::UNSYNCABLE_PREF);
-  prefs->RegisterDoublePref(prefs::kScreenMagnifierScale,
-                            std::numeric_limits<double>::min(),
-                            PrefService::UNSYNCABLE_PREF);
+  if (prefs->FindPreference(prefs::kScreenMagnifierEnabled) == NULL) {
+    prefs->RegisterBooleanPref(prefs::kScreenMagnifierEnabled,
+                               false,
+                               PrefService::UNSYNCABLE_PREF);
+  }
+  if (prefs->FindPreference(prefs::kScreenMagnifierScale) == NULL) {
+    prefs->RegisterDoublePref(prefs::kScreenMagnifierScale,
+                              std::numeric_limits<double>::min(),
+                              PrefService::UNSYNCABLE_PREF);
+  }
   if (prefs->FindPreference(prefs::kVirtualKeyboardEnabled) == NULL) {
     prefs->RegisterBooleanPref(prefs::kVirtualKeyboardEnabled,
                                false,
@@ -283,8 +287,6 @@
       prefs, this);
   natural_scroll_.Init(prefs::kNaturalScroll, prefs, this);
   accessibility_enabled_.Init(prefs::kSpokenFeedbackEnabled, prefs, this);
-  screen_magnifier_enabled_.Init(prefs::kScreenMagnifierEnabled, prefs, this);
-  screen_magnifier_scale_.Init(prefs::kScreenMagnifierScale, prefs, this);
   mouse_sensitivity_.Init(prefs::kMouseSensitivity, prefs, this);
   touchpad_sensitivity_.Init(prefs::kTouchpadSensitivity, prefs, this);
   use_24hour_clock_.Init(prefs::kUse24HourClock, prefs, this);