Introduce incognito preference settings.

chrome/browser/prefs/pref_member.cc

Index: chrome/browser/prefs/pref_member.cc
diff --git a/chrome/browser/prefs/pref_member.cc b/chrome/browser/prefs/pref_member.cc
index cc143846cf710e4604c324148a1a737e62a5eac6..0b3848602783e3681968a2cd3ed32deea81333fc 100644
--- a/chrome/browser/prefs/pref_member.cc
+++ b/chrome/browser/prefs/pref_member.cc
@@ -18,7 +18,7 @@ PrefMemberBase::PrefMemberBase()
 }
 
 PrefMemberBase::~PrefMemberBase() {
-  if (!pref_name_.empty())
+  if (prefs_ && !pref_name_.empty())
     prefs_->RemovePrefObserver(pref_name_.c_str(), this);
 }
 
@@ -37,6 +37,13 @@ void PrefMemberBase::Init(const char* pref_name, PrefService* prefs,
   prefs_->AddPrefObserver(pref_name, this);
 }
 
+void PrefMemberBase::Destroy() {
+  if (prefs_) {
+    prefs_->RemovePrefObserver(pref_name_.c_str(), this);
+    prefs_ = NULL;
+  }
+}
+
 bool PrefMemberBase::IsManaged() const {
   DCHECK(!pref_name_.empty());
   const PrefService::Preference* pref =