Add a CallbackScope class

All credit to Vladimir Kurchatkin, who created the original patch in
nodejs#5691 (comment).

src/node.cc

@@ -1463,6 +1463,14 @@ Local<Value> MakeCallback(Isolate* isolate,
       MakeCallback(env, recv.As<Value>(), callback, argc, argv));
 }
 
+CallbackScope::CallbackScope(Isolate* isolate): isolate_(isolate) {
+}
+
+CallbackScope::~CallbackScope() {
+  Environment* env = Environment::GetCurrent(isolate_);
+  Environment::AsyncCallbackScope callback_scope(env);
+  env->KickNextTick(&callback_scope);
+}
 
 enum encoding ParseEncoding(const char* encoding,
                             enum encoding default_encoding) {

src/node.h

@@ -62,6 +62,7 @@
 
 #include "v8.h"  // NOLINT(build/include_order)
 #include "node_version.h"  // NODE_MODULE_VERSION
+#include "util.h"
 
 #define NODE_MAKE_VERSION(major, minor, patch)                                \
   ((major) * 0x1000 + (minor) * 0x100 + (patch))
@@ -171,6 +172,17 @@ NODE_EXTERN v8::Local<v8::Value> MakeCallback(
     int argc,
     v8::Local<v8::Value>* argv);
 
+class NODE_EXTERN CallbackScope {
+   public:
+    explicit CallbackScope(v8::Isolate* isolate);
+    ~CallbackScope();
+
+   private:
+    v8::Isolate* isolate_;
+
+    DISALLOW_COPY_AND_ASSIGN(CallbackScope);
+};
+
 }  // namespace node
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS