Set new homepage preferences only if there is no existing value.

chrome/browser/browser.cc

 // Copyright (c) 2006-2009 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/browser.h"
 
 #include "app/animation.h"
 #include "app/l10n_util.h"
 #include "base/command_line.h"
 #include "base/idle_timer.h"
@@ skipping 1264 matching lines @@
   GURL url("http://localhost:8080");
   AddTabWithURL(url, GURL(), PageTransition::AUTO_BOOKMARK, true, -1,
                 false, NULL);
 }
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////
 
 // static
 void Browser::SetNewHomePagePrefs(PrefService* prefs) {
-  prefs->SetString(prefs::kHomePage,
-      ASCIIToWide(GoogleURLTracker::kDefaultGoogleHomepage));
-  prefs->SetBoolean(prefs::kHomePageIsNewTabPage, false);
-  prefs->SetBoolean(prefs::kShowHomeButton, true);
+  if (!prefs->HasPrefPath(prefs::kHomePage))
+    prefs->SetString(prefs::kHomePage,
+        ASCIIToWide(GoogleURLTracker::kDefaultGoogleHomepage));
+  if (!prefs->HasPrefPath(prefs::kHomePageIsNewTabPage))
+    prefs->SetBoolean(prefs::kHomePageIsNewTabPage, false);
+  if (!prefs->HasPrefPath(prefs::kShowHomeButton))
+    prefs->SetBoolean(prefs::kShowHomeButton, true);
 }
 
 // static
 void Browser::RegisterPrefs(PrefService* prefs) {
   prefs->RegisterDictionaryPref(prefs::kBrowserWindowPlacement);
   prefs->RegisterIntegerPref(prefs::kOptionsWindowLastTabIndex, 0);
   prefs->RegisterIntegerPref(prefs::kDevToolsSplitLocation, -1);
 }
 
 // static
@@ skipping 1670 matching lines @@
 ///////////////////////////////////////////////////////////////////////////////
 // BrowserToolbarModel (private):
 
 NavigationController* Browser::BrowserToolbarModel::GetNavigationController() {
   // This |current_tab| can be NULL during the initialization of the
   // toolbar during window creation (i.e. before any tabs have been added
   // to the window).
   TabContents* current_tab = browser_->GetSelectedTabContents();
   return current_tab ? &current_tab->controller() : NULL;
 }