Sync: Handle empty (implicit) ParentId in GetPredecessorId and GetSuccessorId

sync/syncable/parent_child_index.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 "sync/syncable/parent_child_index.h"
 
 #include "base/stl_util.h"
 
 #include "sync/syncable/entry_kernel.h"
 #include "sync/syncable/syncable_id.h"
@@ skipping 102 matching lines @@
   ParentChildrenMap::const_iterator parent =
       parent_children_map_.find(parent_id);
   if (parent == parent_children_map_.end()) {
     return false;
   }
   const OrderedChildSet* children = parent->second;
   DCHECK(children && !children->empty());
   return children->count(e) > 0;
 }
 
-const OrderedChildSet* ParentChildIndex::GetChildren(const syncable::Id& id) {
-  ParentChildrenMap::iterator parent = parent_children_map_.find(id);
+const OrderedChildSet* ParentChildIndex::GetChildren(const Id& id) const {
+  DCHECK(!id.IsNull());
+
+  ParentChildrenMap::const_iterator parent = parent_children_map_.find(id);
   if (parent == parent_children_map_.end()) {
     return NULL;
   }
 
   // A successful lookup implies at least some children exist.
   DCHECK(!parent->second->empty());
   return parent->second;
 }
 
+const OrderedChildSet* ParentChildIndex::GetChildren(EntryKernel* e) const {
+  return GetChildren(e->ref(ID));
+}
+
+const OrderedChildSet* ParentChildIndex::GetSiblings(EntryKernel* e) const {
+  DCHECK(Contains(e));
+  const OrderedChildSet* siblings = GetChildren(GetParentId(e));
+  DCHECK(siblings && !siblings->empty());
+  return siblings;
+}
+
 const Id& ParentChildIndex::GetParentId(EntryKernel* e) const {
   const Id& parent_id = e->ref(PARENT_ID);
   if (!parent_id.IsNull()) {
     return parent_id;
   }
   return GetModelTypeRootId(GetModelType(e));
 }
 
 ModelType ParentChildIndex::GetModelType(EntryKernel* e) {
   // TODO(stanisc): is there a more effective way to find out model type?
   ModelType model_type = e->GetModelType();
   if (!syncer::IsRealDataType(model_type)) {
     model_type = e->GetServerModelType();
   }
   return model_type;
 }
 
 const Id& ParentChildIndex::GetModelTypeRootId(ModelType model_type) const {
   // TODO(stanisc): Review whether this approach is reliable enough.
   // Should this method simply enumerate children of root node ("r") instead?
   return model_type_root_ids_[model_type];
 }
 
 }  // namespace syncable
 }  // namespace syncer