Add --hot-reload-test-mode flag to embedder and wire it up to test.py

runtime/vm/isolate_reload.cc

Index: runtime/vm/isolate_reload.cc
diff --git a/runtime/vm/isolate_reload.cc b/runtime/vm/isolate_reload.cc
index d6f1f4c861cf35cc50a1cd562ab9f19c84fbd71b..15aaf2920aa5b1b66cbe38dde6eaeda311330593 100644
--- a/runtime/vm/isolate_reload.cc
+++ b/runtime/vm/isolate_reload.cc
@@ -27,7 +27,10 @@ DEFINE_FLAG(bool, trace_reload, false, "Trace isolate reloading");
 DEFINE_FLAG(bool, identity_reload, false, "Enable checks for identity reload.");
 DEFINE_FLAG(int, reload_every, 0, "Reload every N stack overflow checks.");
 DEFINE_FLAG(bool, reload_every_optimized, true, "Only from optimized code.");
-
+DEFINE_FLAG(bool, reload_every_back_off, false,
+            "Double the --reload-every value after each reload.");
+DEFINE_FLAG(bool, check_reloaded, false,
+            "Assert that an isolate has reloaded at least once.")
 #ifndef PRODUCT
 
 #define I (isolate())