Add ability to change default pref values, and use in BrowserInstantController.

base/prefs/pref_service.cc

Index: base/prefs/pref_service.cc
diff --git a/base/prefs/pref_service.cc b/base/prefs/pref_service.cc
index 67ab898459459bb198cd473711f4183699143bed..745aad3f52ec0f89142f49e952d6759a1da0685d 100644
--- a/base/prefs/pref_service.cc
+++ b/base/prefs/pref_service.cc
@@ -182,8 +182,8 @@ bool PrefService::HasPrefPath(const char* path) const {
 DictionaryValue* PrefService::GetPreferenceValues() const {
   DCHECK(CalledOnValidThread());
   DictionaryValue* out = new DictionaryValue;
-  PrefRegistry::const_iterator i = pref_registry_->begin();
-  for (; i != pref_registry_->end(); ++i) {
+  PrefRegistry::const_iterator i = pref_registry_->defaults()->begin();
+  for (; i != pref_registry_->defaults()->end(); ++i) {
     const Value* value = GetPreferenceValue(i->first);
     DCHECK(value);
     out->Set(i->first, value->DeepCopy());
@@ -273,6 +273,14 @@ const base::Value* PrefService::GetUserPrefValue(const char* path) const {
   return value;
 }
 
+void PrefService::SetDefaultPrefValue(const char* path,
+                                      base::Value* value) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(pref_registry_->defaults()->GetValue(path, NULL))
+      << "Setting default for unregistered pref: " << path;
+  pref_registry_->defaults()->SetDefaultValue(path, value);

[Mattias Nissler (ping if slow), 2013/02/27 10:50:52]

We should CHECK() that the type doesn't change here, and make sure that |value|
!= NULL

[Jói, 2013/02/27 16:30:56]

Done.

+}
+
 const base::Value* PrefService::GetDefaultPrefValue(const char* path) const {
   DCHECK(CalledOnValidThread());
   // Lookup the preference in the default store.
@@ -316,8 +324,8 @@ PrefRegistry* PrefService::DeprecatedGetPrefRegistry() {
 }
 
 void PrefService::AddInitialPreferences() {
-  for (PrefRegistry::const_iterator it = pref_registry_->begin();
-       it != pref_registry_->end();
+  for (PrefRegistry::const_iterator it = pref_registry_->defaults()->begin();
+       it != pref_registry_->defaults()->end();
        ++it) {
     AddRegisteredPreference(it->first.c_str(), it->second);
   }