Take out and generalize user prefs overriding from IncognitoUserPrefStore.

chrome/browser/prefs/incognito_user_pref_store.cc

Index: chrome/browser/prefs/incognito_user_pref_store.cc
diff --git a/chrome/browser/prefs/incognito_user_pref_store.cc b/chrome/browser/prefs/incognito_user_pref_store.cc
index 87bcb2c8870cbd6f2d2c94c5712b3a04e7dec84b..c979cce5845fb76dc2711e13e5bd36a343465c63 100644
--- a/chrome/browser/prefs/incognito_user_pref_store.cc
+++ b/chrome/browser/prefs/incognito_user_pref_store.cc
@@ -3,150 +3,12 @@
 // found in the LICENSE file.
 
 #include "chrome/browser/prefs/incognito_user_pref_store.h"
-
-#include "base/memory/scoped_ptr.h"
-#include "base/values.h"
 #include "chrome/common/pref_names.h"
 
-IncognitoUserPrefStore::IncognitoUserPrefStore(
-    PersistentPrefStore* underlay)
-    : underlay_(underlay) {
-  underlay_->AddObserver(this);
-}
-
-IncognitoUserPrefStore::~IncognitoUserPrefStore() {
-  underlay_->RemoveObserver(this);
-}
-
-bool IncognitoUserPrefStore::IsSetInOverlay(const std::string& key) const {
-  return overlay_.GetValue(key, NULL);
-}
-
-void IncognitoUserPrefStore::AddObserver(PrefStore::Observer* observer) {
-  observers_.AddObserver(observer);
-}
-
-void IncognitoUserPrefStore::RemoveObserver(PrefStore::Observer* observer) {
-  observers_.RemoveObserver(observer);
-}
-
-bool IncognitoUserPrefStore::IsInitializationComplete() const {
-  return underlay_->IsInitializationComplete();
-}
-
-PrefStore::ReadResult IncognitoUserPrefStore::GetValue(
-    const std::string& key,
-    const Value** result) const {
-  // If the |key| shall NOT be stored in the overlay store, there must not
-  // be an entry.
-  DCHECK(ShallBeStoredInOverlay(key) || !overlay_.GetValue(key, NULL));
-
-  if (overlay_.GetValue(key, result))
-    return READ_OK;
-  return underlay_->GetValue(key, result);
-}
-
-PrefStore::ReadResult IncognitoUserPrefStore::GetMutableValue(
-    const std::string& key,
-    Value** result) {
-  if (!ShallBeStoredInOverlay(key))
-    return underlay_->GetMutableValue(key, result);
-
-  if (overlay_.GetValue(key, result))
-    return READ_OK;
-
-  // Try to create copy of underlay if the overlay does not contain a value.
-  Value* underlay_value = NULL;
-  PrefStore::ReadResult read_result =
-      underlay_->GetMutableValue(key, &underlay_value);
-  if (read_result != READ_OK)
-    return read_result;
-
-  *result = underlay_value->DeepCopy();
-  overlay_.SetValue(key, *result);
-  return READ_OK;
-}
-
-void IncognitoUserPrefStore::SetValue(const std::string& key,
-                                      Value* value) {
-  if (!ShallBeStoredInOverlay(key)) {
-    underlay_->SetValue(key, value);
-    return;
-  }
-
-  if (overlay_.SetValue(key, value))
-    ReportValueChanged(key);
-}
-
-void IncognitoUserPrefStore::SetValueSilently(const std::string& key,
-                                              Value* value) {
-  if (!ShallBeStoredInOverlay(key)) {
-    underlay_->SetValueSilently(key, value);
-    return;
-  }
-
-  overlay_.SetValue(key, value);
-}
-
-void IncognitoUserPrefStore::RemoveValue(const std::string& key) {
-  if (!ShallBeStoredInOverlay(key)) {
-    underlay_->RemoveValue(key);
-    return;
-  }
-
-  if (overlay_.RemoveValue(key))
-    ReportValueChanged(key);
-}
-
-bool IncognitoUserPrefStore::ReadOnly() const {
-  return false;
-}
-
-PersistentPrefStore::PrefReadError IncognitoUserPrefStore::ReadPrefs() {
-  // We do not read intentionally.
-  OnInitializationCompleted(true);
-  return PersistentPrefStore::PREF_READ_ERROR_NONE;
-}
-
-void IncognitoUserPrefStore::ReadPrefsAsync(
-    ReadErrorDelegate* error_delegate_raw) {
-  scoped_ptr<ReadErrorDelegate> error_delegate(error_delegate_raw);
-  // We do not read intentionally.
-  OnInitializationCompleted(true);
-}
-
-bool IncognitoUserPrefStore::WritePrefs() {
-  // We do not write our content intentionally.
-  return true;
-}
-
-void IncognitoUserPrefStore::ScheduleWritePrefs() {
-  underlay_->ScheduleWritePrefs();
-  // We do not write our content intentionally.
-}
-
-void IncognitoUserPrefStore::CommitPendingWrite() {
-  underlay_->CommitPendingWrite();
-  // We do not write our content intentionally.
-}
-
-void IncognitoUserPrefStore::ReportValueChanged(const std::string& key) {
-  FOR_EACH_OBSERVER(PrefStore::Observer, observers_, OnPrefValueChanged(key));
-}
-
-void IncognitoUserPrefStore::OnPrefValueChanged(const std::string& key) {
-  if (!overlay_.GetValue(key, NULL))
-    ReportValueChanged(key);
-}
-
-void IncognitoUserPrefStore::OnInitializationCompleted(bool succeeded) {
-  FOR_EACH_OBSERVER(PrefStore::Observer, observers_,
-                    OnInitializationCompleted(succeeded));
-}
-
-bool IncognitoUserPrefStore::ShallBeStoredInOverlay(
-    const std::string& key) const {
+IncognitoUserPrefStore::IncognitoUserPrefStore(PersistentPrefStore* underlay)
+    : OverlayUserPrefStore(underlay) {
   // List of keys that cannot be changed in the user prefs file by the incognito
-  // profile:
-  return key == prefs::kBrowserWindowPlacement;
+  // profile.  All preferences that store information about the browsing history
+  // or behavior of the user should have this property.
+  RegisterOverlayProperty(prefs::kBrowserWindowPlacement);
 }