[Safe Browsing] Use right function to clear preference.

chrome/browser/profiles/profile_impl.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_impl.h"
 
 #include <vector>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 835 matching lines @@
     last_session_exit_type_ =
         SessionTypePrefValueToExitType(exit_type_pref_value);
   }
   // Mark the session as open.
   prefs_->SetString(prefs::kSessionExitType, kPrefExitTypeCrashed);
   // Force this to true in case we fallback and use it.
   // TODO(sky): remove this in a couple of releases (m28ish).
   prefs_->SetBoolean(prefs::kSessionExitedCleanly, true);
 
 #if defined(OS_ANDROID) && defined(FULL_SAFE_BROWSING)
-  // Force safe browsing to false in the case we need to roll back for users
-  // enrolled in Finch trial before.
+  // Clear safe browsing setting in the case we need to roll back
+  // for users enrolled in Finch trial before.
   if (!SafeBrowsingService::IsEnabledByFieldTrial())
-    prefs_->SetBoolean(prefs::kSafeBrowsingEnabled, false);
+    prefs_->ClearPref(prefs::kSafeBrowsingEnabled);
 #endif
 
   g_browser_process->profile_manager()->InitProfileUserPrefs(this);
 
   BrowserContextDependencyManager::GetInstance()->CreateBrowserContextServices(
       this);
 
   DCHECK(!net_pref_observer_);
   {
     TRACE_EVENT0("browser", "ProfileImpl::OnPrefsLoaded:NetPrefObserver")
@@ skipping 449 matching lines @@
 ProfileImpl::CreateDomainReliabilityMonitor() {
   domain_reliability::DomainReliabilityService* service =
       domain_reliability::DomainReliabilityServiceFactory::GetInstance()->
           GetForBrowserContext(this);
   if (!service)
     return scoped_ptr<domain_reliability::DomainReliabilityMonitor>();
 
   return service->CreateMonitor(
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO));
 }