Merge pull request #4280 from ctiller/import-sadness

Fix for when grpc::string is not the same type as FLAGS_...

test/cpp/interop/metrics_client.cc

@@ -50,7 +50,7 @@ using grpc::testing::GaugeResponse;
 using grpc::testing::MetricsService;
 using grpc::testing::MetricsServiceImpl;
 
-void PrintMetrics(grpc::string& server_address) {
+void PrintMetrics(const grpc::string& server_address) {
   gpr_log(GPR_INFO, "creating a channel to %s", server_address.c_str());
   std::shared_ptr<grpc::Channel> channel(
       grpc::CreateChannel(server_address, grpc::InsecureChannelCredentials()));