Document some recent service protocol features

runtime/vm/json_stream.cc

Index: runtime/vm/json_stream.cc
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 7bbdc6fb24c4286a65406b4bd9e5a82bd553c88f..f098998dd1642b3e05d87986cef481144d79e2c0 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -150,8 +150,8 @@ static const char* GetJSONRpcErrorMessage(intptr_t code) {
       return "File system does not exist";
     case kFileDoesNotExist:
       return "File does not exist";
-    case kIsolateReloadFailed:
-      return "Isolate reload failed";
+    case kIsolateReloadBarred:
+      return "Isolate cannot be reloaded";
     default:
       return "Extension error";
   }