Add a command line flag to disable streaming.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index f906aa9b180aa151d671deabf9a5bfb8be279e39..10cf774238385a309dbcbdf524e57d6ffa6adf3a 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -589,6 +589,9 @@ DEFINE_MAYBE_BOOL(enable_armv8, "deprecated (use --arm_arch instead)")
 DEFINE_BOOL(enable_regexp_unaligned_accesses, true,
             "enable unaligned accesses for the regexp engine")
 
+// api.cc
+DEFINE_BOOL(script_streaming, true, "enable parsing on background")
+
 // bootstrapper.cc
 DEFINE_STRING(expose_natives_as, NULL, "expose natives in global object")
 DEFINE_STRING(expose_debug_as, NULL, "expose debug in global object")