Add basic GL functionality to the passthrough command buffer.

gpu/command_buffer/service/client_service_map.h

Index: gpu/command_buffer/service/client_service_map.h
diff --git a/gpu/command_buffer/service/client_service_map.h b/gpu/command_buffer/service/client_service_map.h
new file mode 100644
index 0000000000000000000000000000000000000000..14a914cdeef67d6d5c841b837e0006d4d96bdb13
--- /dev/null
+++ b/gpu/command_buffer/service/client_service_map.h
@@ -0,0 +1,72 @@
+// Copyright (c) 2016 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_CLIENT_SERVICE_MAP_H_
+#define GPU_COMMAND_BUFFER_SERVICE_CLIENT_SERVICE_MAP_H_
+
+#include <limits>
+#include <unordered_map>
+
+namespace gpu {
+
+namespace gles2 {
+
+template <typename ClientType, typename ServiceType>
+class ClientServiceMap {
+ public:
+  ClientServiceMap()
+      : client_to_service_(),
+        next_service_reserved_index_(std::numeric_limits<ServiceType>::max()) {}
+
+  void SetIDMapping(ClientType client_id, ServiceType service_id) {
+    DCHECK(client_to_service_.find(client_id) == client_to_service_.end());
+    client_to_service_[client_id] = service_id;
+  }
+
+  void RemoveClientID(ClientType client_id) {
+    client_to_service_.erase(client_id);
+  }
+
+  bool GetServiceID(ClientType client_id, ServiceType* service_id) const {
+    if (client_id == 0) {
+      if (service_id) {
+        *service_id = 0;
+      }
+      return true;
+    }
+    auto iter = client_to_service_.find(client_id);
+    if (iter != client_to_service_.end()) {
+      if (service_id) {
+        *service_id = iter->second;
+      }
+      return true;
+    } else {

[Zhenyao Mo, 2016/09/09 21:22:10]

nit: chrome style asks no else here.

[Geoff Lang, 2016/09/12 14:21:29]

Done.

+      return false;
+    }
+  }
+
+  ServiceType ReserveClientID(ClientType client_id) {
+    ServiceType service_id = next_service_reserved_index_--;
+    SetIDMapping(client_id, service_id);
+    return service_id;
+  }
+
+  ServiceType GetServiceIDOrReserve(ClientType client_id) {
+    ServiceType service_id;
+    if (GetServiceID(client_id, &service_id)) {
+      return service_id;
+    } else {

[Zhenyao Mo, 2016/09/09 21:22:10]

Same here, no else

[Geoff Lang, 2016/09/12 14:21:29]

Done.

+      return ReserveClientID(client_id);
+    }
+  }
+
+ private:
+  std::unordered_map<ClientType, ServiceType> client_to_service_;
+  ServiceType next_service_reserved_index_;
+};
+
+}  // namespace gles2
+}  // namespace gpu
+
+#endif  // GPU_COMMAND_BUFFER_SERVICE_CLIENT_SERVICE_MAP_H_