Introduce a temporary workaround to ensure tracked preferences set to empty list/dict are not confu…

base/prefs/pref_service.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 "base/prefs/pref_service.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/files/file_path.h"
@@ skipping 279 matching lines @@
   DCHECK(CalledOnValidThread());
   // Lookup the preference in the default store.
   const base::Value* value = NULL;
   if (!pref_registry_->defaults()->GetValue(path, &value)) {
     NOTREACHED() << "Default value missing for pref: " << path;
     return NULL;
   }
   return value;
 }
 
+void PrefService::MarkUserStoreNeedsEmptyValue(const std::string& key) const {
+  user_pref_store_->MarkNeedsEmptyValue(key);
+}
+
 const base::ListValue* PrefService::GetList(const char* path) const {
   DCHECK(CalledOnValidThread());
 
   const base::Value* value = GetPreferenceValue(path);
   if (!value) {
     NOTREACHED() << "Trying to read an unregistered pref: " << path;
     return NULL;
   }
   if (value->GetType() != base::Value::TYPE_LIST) {
     NOTREACHED();
@@ skipping 280 matching lines @@
       DCHECK(found_value->IsType(default_type));
       return found_value;
     } else {
       // Every registered preference has at least a default value.
       NOTREACHED() << "no valid value found for registered pref " << path;
     }
   }
 
   return NULL;
 }