gpu: Add SequenceId for identifying sync point sequences.

gpu/command_buffer/service/sequence_id.h

Index: gpu/command_buffer/service/sequence_id.h
diff --git a/gpu/command_buffer/service/sequence_id.h b/gpu/command_buffer/service/sequence_id.h
new file mode 100644
index 0000000000000000000000000000000000000000..a2302c2ae9e7d233a954f7c8d5646f125b13e563
--- /dev/null
+++ b/gpu/command_buffer/service/sequence_id.h
@@ -0,0 +1,17 @@
+// 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.
+
+#ifndef GPU_COMMAND_BUFFER_SERVICE_SEQUENCE_ID_H_
+#define GPU_COMMAND_BUFFER_SERVICE_SEQUENCE_ID_H_
+
+#include "gpu/command_buffer/common/id_type.h"
+
+namespace gpu {
+
+class SyncPointOrderData;
+using SequenceId = gpu::IdTypeU32<SyncPointOrderData>;
+
+}  // namespace gpu
+
+#endif  // GPU_COMMAND_BUFFER_SERVICE_SEQUENCE_ID_H_