Make assertion scopes thread safe.

src/checks.cc

Index: src/checks.cc
diff --git a/src/checks.cc b/src/checks.cc
index 8bcde1c61ce751650d7dd7385396c33ede57dc72..82086824dd2ba6e64cbb8c2339c170e073ab61d7 100644
--- a/src/checks.cc
+++ b/src/checks.cc
@@ -36,6 +36,8 @@ static int fatal_error_handler_nesting_depth = 0;
 
 // Contains protection against recursive calls (faults while handling faults).
 extern "C" void V8_Fatal(const char* file, int line, const char* format, ...) {
+  i::AllowHandleDereference allow_deref;
+  i::AllowDeferredHandleDereference allow_deferred_deref;
   fflush(stdout);
   fflush(stderr);
   fatal_error_handler_nesting_depth++;