Do not pass NULL to GetAsString().

chrome/browser/ui/ash/launcher/chrome_launcher_controller_per_browser.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/ui/ash/launcher/chrome_launcher_controller_per_browser.h"
 
 #include <vector>
 
 #include "ash/launcher/launcher_model.h"
 #include "ash/shell.h"
@@ skipping 176 matching lines @@
     const base::DictionaryValue* shelf_prefs = pref_service->GetDictionary(
         prefs::kShelfPreferences);
     const base::DictionaryValue* display_pref = NULL;
     std::string per_display_value;
     if (shelf_prefs->GetDictionary(pref_key, &display_pref) &&
         display_pref->GetString(path, &per_display_value))
       return per_display_value;
 
     // If the pref for the specified display is not found, scan the whole prefs
     // and check if the prefs for other display is already specified.
+    std::string unused_value;
     for (base::DictionaryValue::Iterator iter(*shelf_prefs);
          !iter.IsAtEnd(); iter.Advance()) {
       const base::DictionaryValue* display_pref = NULL;
       if (iter.value().GetAsDictionary(&display_pref) &&
-          display_pref->GetString(path, static_cast<std::string*>(NULL))) {
+          display_pref->GetString(path, &unused_value)) {
         has_per_display_prefs = true;
         break;
       }
     }
   }
 
   if (local_pref->IsRecommended() || !has_per_display_prefs)
     return value;
 
   const base::Value* default_value =
@@ skipping 1083 matching lines @@
 void ChromeLauncherControllerPerBrowser::SetAppIconLoaderForTest(
     ash::AppIconLoader* loader) {
   app_icon_loader_.reset(loader);
 }
 
 const std::string&
 ChromeLauncherControllerPerBrowser::GetAppIdFromLauncherIdForTest(
     ash::LauncherID id) {
   return id_to_item_controller_map_[id]->app_id();
 }