Add subscribe to VHAL proto.

The latest IVehicleHardware adds Subscribe/Unsubscribe function
to replace the existing updateSampleRate. This CL adds the
Subscribe function to protobuf definition and implements it.

Test: atest GRPCVehicleHardwareUnitTest GRPCVehicleProxyServerUnitTest
Flag: EXEMPT hal change
Bug: 328316981
Merged-In: I4f02885b77f21a215a8b282be583f76118e400ba
(cherry-picked from commit: f1a869055fcd6ea980e329e86d71ace715427d30)

Change-Id: I4f02885b77f21a215a8b282be583f76118e400ba
diff --git a/automotive/vehicle/aidl/impl/grpc/GRPCVehicleHardware.cpp b/automotive/vehicle/aidl/impl/grpc/GRPCVehicleHardware.cpp
index 0742283..2e5d2e4 100644
--- a/automotive/vehicle/aidl/impl/grpc/GRPCVehicleHardware.cpp
+++ b/automotive/vehicle/aidl/impl/grpc/GRPCVehicleHardware.cpp
@@ -39,6 +39,13 @@
       mGrpcStub(proto::VehicleServer::NewStub(mGrpcChannel)),
       mValuePollingThread([this] { ValuePollingLoop(); }) {}
 
+// Only used for unit testing.
+GRPCVehicleHardware::GRPCVehicleHardware(std::unique_ptr<proto::VehicleServer::StubInterface> stub)
+    : mServiceAddr(""),
+      mGrpcChannel(nullptr),
+      mGrpcStub(std::move(stub)),
+      mValuePollingThread([] {}) {}
+
 GRPCVehicleHardware::~GRPCVehicleHardware() {
     {
         std::lock_guard lck(mShutdownMutex);
@@ -181,6 +188,24 @@
     return static_cast<aidlvhal::StatusCode>(protoStatus.status_code());
 }
 
+aidlvhal::StatusCode GRPCVehicleHardware::subscribe(aidlvhal::SubscribeOptions options) {
+    proto::SubscribeRequest request;
+    ::grpc::ClientContext context;
+    proto::VehicleHalCallStatus protoStatus;
+    proto_msg_converter::aidlToProto(options, request.mutable_options());
+    auto grpc_status = mGrpcStub->Subscribe(&context, request, &protoStatus);
+    if (!grpc_status.ok()) {
+        if (grpc_status.error_code() == ::grpc::StatusCode::UNIMPLEMENTED) {
+            // This is a legacy sever. It should handle updateSampleRate.
+            LOG(INFO) << __func__ << ": GRPC Subscribe is not supported by the server";
+            return aidlvhal::StatusCode::OK;
+        }
+        LOG(ERROR) << __func__ << ": GRPC Subscribe Failed: " << grpc_status.error_message();
+        return aidlvhal::StatusCode::INTERNAL_ERROR;
+    }
+    return static_cast<aidlvhal::StatusCode>(protoStatus.status_code());
+}
+
 aidlvhal::StatusCode GRPCVehicleHardware::updateSampleRate(int32_t propId, int32_t areaId,
                                                            float sampleRate) {
     ::grpc::ClientContext context;