Optimize writes upon ProfileManager::UpdateLastUser.

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 1314 matching lines @@
 ProfileManager::ProfileInfo::~ProfileInfo() {
   ProfileDestroyer::DestroyProfileWhenAppropriate(profile.release());
 }
 
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
 void ProfileManager::UpdateLastUser(Profile* last_active) {
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);
   // Only keep track of profiles that we are managing; tests may create others.
   if (profiles_info_.find(last_active->GetPath()) != profiles_info_.end()) {
-    local_state->SetString(prefs::kProfileLastUsed,
-                           last_active->GetPath().BaseName().MaybeAsASCII());
+    std::string profile_path_base =
+        last_active->GetPath().BaseName().MaybeAsASCII();
+    if (profile_path_base != local_state->GetString(prefs::kProfileLastUsed))
+      local_state->SetString(prefs::kProfileLastUsed, profile_path_base);
 
     ProfileInfoCache& cache = GetProfileInfoCache();
     size_t profile_index =
         cache.GetIndexOfProfileWithPath(last_active->GetPath());
     if (profile_index != std::string::npos)
       cache.SetProfileActiveTimeAtIndex(profile_index);
   }
 }
 
 ProfileManager::BrowserListObserver::BrowserListObserver(
@@ skipping 70 matching lines @@
   }
 
   FinishDeletingProfile(profile_to_delete_path, new_active_profile_path);
   if (!original_callback.is_null())
     original_callback.Run(loaded_profile, status);
 }
 
 ProfileManagerWithoutInit::ProfileManagerWithoutInit(
     const base::FilePath& user_data_dir) : ProfileManager(user_data_dir) {
 }