Guest profile should reset the default search provider.

chrome/browser/profiles/profile_manager.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/profiles/profile_manager.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 1184 matching lines @@
     cache.SetProfileIsEphemeralAtIndex(
         cache.GetIndexOfProfileWithPath(profile->GetPath()), true);
   }
 }
 
 void ProfileManager::SetGuestProfilePrefs(Profile* profile) {
   PrefService* prefs = profile->GetPrefs();
   prefs->SetBoolean(prefs::kSigninAllowed, false);
   prefs->SetBoolean(bookmarks::prefs::kEditBookmarksEnabled, false);
   prefs->SetBoolean(bookmarks::prefs::kShowBookmarkBar, false);
+  prefs->ClearPref(DefaultSearchManager::kDefaultSearchProviderDataPrefName);
   // This can be removed in the future but needs to be present through
   // a release (or two) so that any existing installs get switched to
   // the new state and away from the previous "forced" state.
   IncognitoModePrefs::SetAvailability(prefs, IncognitoModePrefs::ENABLED);
 }
 
 bool ProfileManager::ShouldGoOffTheRecord(Profile* profile) {
 #if defined(OS_CHROMEOS)
   if (profile->GetPath().BaseName().value() == chrome::kInitialProfile) {
     return true;
@@ skipping 113 matching lines @@
           last_non_supervised_profile_path.BaseName().MaybeAsASCII());
       FinishDeletingProfile(profile_to_delete_path);
     }
   }
 }
 #endif
 
 ProfileManagerWithoutInit::ProfileManagerWithoutInit(
     const base::FilePath& user_data_dir) : ProfileManager(user_data_dir) {
 }