Add DBus hiding client library

This library hides update_engine's legacy DBus dependencies until we
can remove them completely.

Bug: 24547247
Test: mmm system/update_engine; emerge-panther update_engine

Change-Id: I7f87f2a7c31d0940c376ef43368e53b0f3bc3407
diff --git a/client_library/client.cc b/client_library/client.cc
new file mode 100644
index 0000000..d6e7382
--- /dev/null
+++ b/client_library/client.cc
@@ -0,0 +1,31 @@
+//
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "update_engine/client_library/include/update_engine/client.h"
+
+#include <memory>
+
+#include "update_engine/client_library/client_impl.h"
+
+using std::unique_ptr;
+
+namespace update_engine {
+
+std::unique_ptr<UpdateEngineClient> UpdateEngineClient::CreateInstance() {
+  return unique_ptr<UpdateEngineClient>{new internal::UpdateEngineClientImpl{}};
+}
+
+}  // namespace update_engine