Add ostream support for string_ref

include/grpc++/support/string_ref.h

@@ -35,6 +35,7 @@
 #define GRPCXX_STRING_REF_H
 
 #include <iterator>
+#include <iosfwd>
 
 #include <grpc++/support/config.h>
 
@@ -110,6 +111,8 @@ bool operator>(string_ref x, string_ref y);
 bool operator<=(string_ref x, string_ref y);
 bool operator>=(string_ref x, string_ref y);
 
+std::ostream& operator<<(std::ostream& stream, const string_ref& string);
+
 }  // namespace grpc
 
 #endif  // GRPCXX_STRING_REF_H

src/cpp/util/string_ref.cc

@@ -108,4 +108,8 @@ bool operator>=(string_ref x, string_ref y) {
   return x.compare(y) >= 0;
 }
 
+std::ostream& operator<<(std::ostream& out, const string_ref& string) {
+  return out << grpc::string(string.begin(), string.end());
+}
+
 }  // namespace grpc