Merge pull request #8118 from stanley-cheung/cpp-examples-missing-gpr-asserts

cpp examples missing gpr asserts
diff --git a/examples/cpp/helloworld/greeter_async_client.cc b/examples/cpp/helloworld/greeter_async_client.cc
index 33de59f..595baae 100644
--- a/examples/cpp/helloworld/greeter_async_client.cc
+++ b/examples/cpp/helloworld/greeter_async_client.cc
@@ -36,6 +36,7 @@
 #include <string>
 
 #include <grpc++/grpc++.h>
+#include <grpc/support/log.h>
 
 #include "helloworld.grpc.pb.h"
 
diff --git a/examples/cpp/helloworld/greeter_async_client2.cc b/examples/cpp/helloworld/greeter_async_client2.cc
index 0902376..fe0a213 100644
--- a/examples/cpp/helloworld/greeter_async_client2.cc
+++ b/examples/cpp/helloworld/greeter_async_client2.cc
@@ -36,6 +36,7 @@
 #include <string>
 
 #include <grpc++/grpc++.h>
+#include <grpc/support/log.h>
 #include <thread>
 
 #include "helloworld.grpc.pb.h"
diff --git a/examples/cpp/helloworld/greeter_async_server.cc b/examples/cpp/helloworld/greeter_async_server.cc
index ead4418..bd14b0e 100644
--- a/examples/cpp/helloworld/greeter_async_server.cc
+++ b/examples/cpp/helloworld/greeter_async_server.cc
@@ -37,6 +37,7 @@
 #include <thread>
 
 #include <grpc++/grpc++.h>
+#include <grpc/support/log.h>
 
 #include "helloworld.grpc.pb.h"