Pref service: add a factory to create the client lib

services/preferences/public/cpp/pref_store_manager_impl.cc

 // Copyright 2017 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 "services/preferences/public/cpp/pref_store_manager_impl.h"
 
 #include <utility>
 
 #include "base/memory/ref_counted.h"
 #include "base/threading/sequenced_worker_pool.h"
@@ skipping 40 matching lines @@
 };
 
 // static
 void ConnectionBarrier::Create(const PrefStorePtrs& pref_store_ptrs,
                                const ConnectCallback& callback) {
   make_scoped_refptr(new ConnectionBarrier(pref_store_ptrs, callback))
       ->Init(pref_store_ptrs);
 }
 
 void ConnectionBarrier::Init(const PrefStorePtrs& pref_store_ptrs) {
+  if (expected_connections_ == 0) {
+    // Degenerate case. We don't expect this, but it could happen in
+    // e.g. testing.
+    callback_.Run(std::move(connections_));
+    return;
+  }
   for (const auto& ptr : pref_store_ptrs) {
     ptr.second->AddObserver(
         base::Bind(&ConnectionBarrier::OnConnect, this, ptr.first));
   }
 }
 
 ConnectionBarrier::ConnectionBarrier(const PrefStorePtrs& pref_store_ptrs,
                                      const ConnectCallback& callback)
     : callback_(callback), expected_connections_(pref_store_ptrs.size()) {}
 
@@ skipping 114 matching lines @@
     PrefValueStore::PrefStoreType type) {
   DVLOG(1) << "Deregistering pref store: " << type;
   pref_store_ptrs_.erase(type);
 }
 
 bool PrefStoreManagerImpl::AllConnected() const {
   return pref_store_ptrs_.size() == expected_pref_stores_.size();
 }
 
 }  // namespace prefs