Add a command line flag to disable streaming.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 8ab362ae205e76a19b436dc8740455da0d75b7ff..ded99d2b7a92363d6e7d7aea8da9f3ab6c7481cf 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -2215,6 +2215,9 @@ Local<Function> ScriptCompiler::CompileFunctionInContext(
 
 ScriptCompiler::ScriptStreamingTask* ScriptCompiler::StartStreamingScript(
     Isolate* v8_isolate, StreamedSource* source, CompileOptions options) {
+  if (!i::FLAG_script_streaming) {
+    return nullptr;
+  }
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(v8_isolate);
   return new i::BackgroundParsingTask(source->impl(), options,
                                       i::FLAG_stack_size, isolate);