[Sync] Make GetFirstChildId return a flag indicating success

chrome/browser/sync/internal_api/change_reorder_buffer.cc

 // Copyright (c) 2011 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 "chrome/browser/sync/internal_api/change_reorder_buffer.h"
 
 #include <limits>
 #include <queue>
 #include <set>
 #include <utility>  // for pair<>
@@ skipping 103 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(Traversal);
 };
 
 ChangeReorderBuffer::ChangeReorderBuffer() {
 }
 
 ChangeReorderBuffer::~ChangeReorderBuffer() {
 }
 
-ImmutableChangeRecordList ChangeReorderBuffer::GetAllChangesInTreeOrder(
-    const BaseTransaction* sync_trans) {
+bool ChangeReorderBuffer::GetAllChangesInTreeOrder(
+    const BaseTransaction* sync_trans,
+    ImmutableChangeRecordList* changes) {
   syncable::BaseTransaction* trans = sync_trans->GetWrappedTrans();
 
   // Step 1: Iterate through the operations, doing three things:
   // (a) Push deleted items straight into the |changelist|.
   // (b) Construct a traversal spanning all non-deleted items.
   // (c) Construct a set of all parent nodes of any position changes.
   set<int64> parents_of_position_changes;
   Traversal traversal;
 
   ChangeRecordList changelist;
@@ skipping 57 matching lines @@
         Traversal::LinkSet::const_iterator j = traversal.begin_children(next);
         Traversal::LinkSet::const_iterator end = traversal.end_children(next);
         for (; j != end; ++j) {
           CHECK(j->first == next);
           to_visit.push(j->second);
         }
     } else {
       // There were ordering changes on the children of this parent, so
       // enumerate all the children in the sibling order.
       syncable::Entry parent(trans, syncable::GET_BY_HANDLE, next);
-      syncable::Id id = trans->directory()->
-          GetFirstChildId(trans, parent.Get(syncable::ID));
+      syncable::Id id;
+      if (!trans->directory()->GetFirstChildId(
+              trans, parent.Get(syncable::ID), &id)) {
+        *changes = ImmutableChangeRecordList();
+        return false;
+      }
       while (!id.IsRoot()) {
         syncable::Entry child(trans, syncable::GET_BY_ID, id);
         CHECK(child.good());
         int64 handle = child.Get(syncable::META_HANDLE);
         to_visit.push(handle);
         // If there is no operation on this child node, record it as as an
         // update, so that the listener gets notified of all nodes in the new
         // ordering.
         if (operations_.find(handle) == operations_.end())
           operations_[handle] = OP_UPDATE_POSITION_AND_PROPERTIES;
         id = child.Get(syncable::NEXT_ID);
       }
     }
   }
 
-  return ImmutableChangeRecordList(&changelist);
+  *changes = ImmutableChangeRecordList(&changelist);
+  return true;
 }
 
 }  // namespace sync_api