Roll forward to cl/314747126

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: Ie19e006429b138b3768e97dae971a43fdc5ef8bf

cpp/platform/impl/g3/system_clock_impl.h

@@ -0,0 +1,37 @@
+// Copyright 2020 Google LLC
+//
+// 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
+//
+//     https://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 PLATFORM_IMPL_G3_SYSTEM_CLOCK_IMPL_H_
+#define PLATFORM_IMPL_G3_SYSTEM_CLOCK_IMPL_H_
+
+#include <cstdint>
+
+#include "platform/api/system_clock.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+
+namespace location {
+namespace nearby {
+
+class SystemClockImpl : public SystemClock {
+ public:
+  std::int64_t elapsedRealtime() override {
+    return absl::ToUnixMillis(absl::Now());
+  }
+};
+
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_G3_SYSTEM_CLOCK_IMPL_H_