Adding Google benchmarking library.

third_party/google_benchmark/include/benchmark/benchmark.h

Index: third_party/google_benchmark/include/benchmark/benchmark.h
diff --git a/third_party/google_benchmark/include/benchmark/benchmark.h b/third_party/google_benchmark/include/benchmark/benchmark.h
new file mode 100644
index 0000000000000000000000000000000000000000..b3b0a8e947fb4cf9f5ebe3375f8f597f0897343f
--- /dev/null
+++ b/third_party/google_benchmark/include/benchmark/benchmark.h
@@ -0,0 +1,21 @@
+// Copyright 2015 Google Inc. All rights reserved.
+//
+// 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.
+#ifndef BENCHMARK_BENCHMARK_H_
+#define BENCHMARK_BENCHMARK_H_
+
+#include "benchmark_api.h"
+#include "macros.h"
+#include "reporter.h"
+
+#endif  // BENCHMARK_BENCHMARK_H_