Add new reasons for server restart: PID_FILE_BUT_NO_SERVER, SERVER_VANISHED and SERVER_UNRESPONSIVE, since it looks like these are happening with upsetting frequency in our new grpc world.

PiperOrigin-RevId: 156271743
diff --git a/src/main/cpp/global_variables.h b/src/main/cpp/global_variables.h
index 063cdbb..4774f29 100644
--- a/src/main/cpp/global_variables.h
+++ b/src/main/cpp/global_variables.h
@@ -31,7 +31,15 @@
 
 // The reason for a blaze server restart.
 // Keep in sync with logging.proto.
-enum RestartReason { NO_RESTART = 0, NO_DAEMON, NEW_VERSION, NEW_OPTIONS };
+enum RestartReason {
+  NO_RESTART = 0,
+  NO_DAEMON,
+  NEW_VERSION,
+  NEW_OPTIONS,
+  PID_FILE_BUT_NO_SERVER,
+  SERVER_VANISHED,
+  SERVER_UNRESPONSIVE
+};
 
 struct GlobalVariables {
   GlobalVariables(OptionProcessor *option_processor);