[Sync] Add HasChildren() function and use it instead of GetFirstChildId()

chrome/browser/sync/glue/session_model_associator.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/glue/session_model_associator.h"
 
 #include <algorithm>
 #include <set>
 #include <utility>
 
@@ skipping 83 matching lines @@
   CHECK(has_nodes);
   *has_nodes = false;
   sync_api::ReadTransaction trans(FROM_HERE, sync_service_->GetUserShare());
   sync_api::ReadNode root(&trans);
   if (!root.InitByTagLookup(kSessionsTag)) {
     LOG(ERROR) << kNoSessionsFolderError;
     return false;
   }
   // The sync model has user created nodes iff the sessions folder has
   // any children.
-  *has_nodes = root.GetFirstChildId() != sync_api::kInvalidId;
+  *has_nodes = root.HasChildren();
   return true;
 }
 
 int64 SessionModelAssociator::GetSyncIdFromChromeId(const size_t& id) {
   DCHECK(CalledOnValidThread());
   return GetSyncIdFromSessionTag(TabIdToTag(GetCurrentMachineTag(), id));
 }
 
 int64 SessionModelAssociator::GetSyncIdFromSessionTag(const std::string& tag) {
   DCHECK(CalledOnValidThread());
@@ skipping 1169 matching lines @@
   char computer_name[MAX_COMPUTERNAME_LENGTH + 1];
   DWORD size = sizeof(computer_name);
   if (GetComputerNameA(computer_name, &size)) {
     return computer_name;
   }
   return std::string();
 }
 #endif
 
 }  // namespace browser_sync