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

chrome/browser/chromeos/preferences.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/preferences.h"
 
 #include "base/chromeos/chromeos_version.h"
 #include "base/command_line.h"
 #include "base/i18n/time_formatting.h"
 #include "base/metrics/histogram.h"
@@ skipping 79 matching lines @@
   if (prefs->FindPreference(prefs::kSpokenFeedbackEnabled) == NULL) {
     prefs->RegisterBooleanPref(prefs::kSpokenFeedbackEnabled,
                                false,
                                PrefService::UNSYNCABLE_PREF);
   }
   if (prefs->FindPreference(prefs::kHighContrastEnabled) == NULL) {
     prefs->RegisterBooleanPref(prefs::kHighContrastEnabled,
                                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,
                                PrefService::UNSYNCABLE_PREF);
   }
   prefs->RegisterIntegerPref(prefs::kMouseSensitivity,
                              3,
                              PrefService::UNSYNCABLE_PREF);
   prefs->RegisterIntegerPref(prefs::kTouchpadSensitivity,
                              3,
@@ skipping 160 matching lines @@
 }
 
 void Preferences::InitUserPrefs(PrefService* prefs) {
   prefs_ = prefs;
 
   tap_to_click_enabled_.Init(prefs::kTapToClickEnabled, prefs, this);
   three_finger_click_enabled_.Init(prefs::kEnableTouchpadThreeFingerClick,
       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);
   disable_drive_.Init(prefs::kDisableGData, prefs, this);
   disable_drive_over_cellular_.Init(prefs::kDisableGDataOverCellular,
                                    prefs, this);
   disable_drive_hosted_files_.Init(prefs::kDisableGDataHostedFiles,
                                    prefs, this);
   download_default_directory_.Init(prefs::kDownloadDefaultDirectory,
                                    prefs, this);
@@ skipping 431 matching lines @@
 
   input_method::AutoRepeatRate rate;
   rate.initial_delay_in_ms = xkb_auto_repeat_delay_pref_.GetValue();
   rate.repeat_interval_in_ms = xkb_auto_repeat_interval_pref_.GetValue();
   DCHECK(rate.initial_delay_in_ms > 0);
   DCHECK(rate.repeat_interval_in_ms > 0);
   input_method::XKeyboard::SetAutoRepeatRate(rate);
 }
 
 }  // namespace chromeos