Replace std::function with base::Closure

std::function doesn't support non-copyable arguments. Use base::Closure
and base::OnceClosure from libchrome instead.

Test: atest --host bluetooth_test_gd
Change-Id: Ic18bbc000730e8b0d7acff0097870bd258ee6150
diff --git a/gd/common/callback.h b/gd/common/callback.h
new file mode 100644
index 0000000..b8be642
--- /dev/null
+++ b/gd/common/callback.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright 2019 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.
+ */
+
+#pragma once
+
+#include "base/callback.h"
+
+namespace bluetooth {
+namespace common {
+
+using base::Callback;
+using base::Closure;
+using base::OnceCallback;
+using base::OnceClosure;
+
+}  // namespace common
+}  // namespace bluetooth