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

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index bd26039f1e8b524f271d2dc1c6a53b41cff88847..9dfb0522a20aea1ace535873464bd7d839a92b74 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -55,6 +55,7 @@ DECLARE_FLAG(bool, timing);
 DECLARE_FLAG(bool, trace_service);
 DECLARE_FLAG(bool, trace_reload);
 DECLARE_FLAG(bool, warn_on_pause_with_no_debugger);
+DECLARE_FLAG(bool, check_reloaded);
 
 NOT_IN_PRODUCT(
 static void CheckedModeHandler(bool value) {
@@ -1693,6 +1694,15 @@ void Isolate::Shutdown() {
     }
   }
 
+  if (FLAG_check_reloaded &&
+      !ServiceIsolate::IsServiceIsolateDescendant(this)) {
+    if (!HasAttemptedReload()) {
+      OS::PrintErr("Isolate did not reload before exiting and "

[rmacnak, 2016/07/01 20:53:22]

FATAL("...")

[Cutch, 2016/07/01 21:26:40]

Done.

+                   "--check-reloaded is enabled.\n");
+      UNREACHABLE();
+    }
+  }
+
   // Then, proceed with low-level teardown.
   LowLevelShutdown();