Allow optional building in of objc prefix validation. (#28388)

src/compiler/objective_c_plugin.cc

@@ -29,6 +29,9 @@
 using ::google::protobuf::compiler::objectivec::
     IsProtobufLibraryBundledProtoFile;
 using ::google::protobuf::compiler::objectivec::ProtobufLibraryFrameworkName;
+#ifdef SUPPORT_OBJC_PREFIX_VALIDATION
+using ::google::protobuf::compiler::objectivec::ValidateObjCClassPrefixes;
+#endif
 using ::grpc_objective_c_generator::FrameworkImport;
 using ::grpc_objective_c_generator::LocalImport;
 using ::grpc_objective_c_generator::PreprocIfElse;
@@ -90,6 +93,13 @@ class ObjectiveCGrpcGenerator : public grpc::protobuf::compiler::CodeGenerator {
       return true;
     }
 
+#ifdef SUPPORT_OBJC_PREFIX_VALIDATION
+    // Default options will use env variables for controls.
+    if (!ValidateObjCClassPrefixes({file}, {}, error)) {
+      return false;
+    }
+#endif
+
     bool grpc_local_import = false;
     ::std::string framework;
     ::std::string pb_runtime_import_prefix;