node: Add signature to SET_PROTOTYPE_METHOD.

This prevents segfaults when a native method is reassigned to a
different object (which corrupts `args.This()`).  When unwrapping,
clients should use `args.Holder()` instead of `args.This()`.

Closes nodejs#6690.

Author: cscott

doc/api/addons.markdown

@@ -401,7 +401,7 @@ prototype:
       Isolate* isolate = Isolate::GetCurrent();
       HandleScope scope(isolate);
 
-      MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.This());
+      MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
       obj->value_ += 1;
 
       args.GetReturnValue().Set(Number::New(isolate, obj->value_));
@@ -539,7 +539,7 @@ The implementation is similar to the above in `myobject.cc`:
       Isolate* isolate = Isolate::GetCurrent();
       HandleScope scope(isolate);
 
-      MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.This());
+      MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
       obj->value_ += 1;
 
       args.GetReturnValue().Set(Number::New(isolate, obj->value_));

src/fs_event_wrap.cc

@@ -106,7 +106,7 @@ void FSEventWrap::Start(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args.GetIsolate());
   HandleScope scope(env->isolate());
 
-  FSEventWrap* wrap = Unwrap<FSEventWrap>(args.This());
+  FSEventWrap* wrap = Unwrap<FSEventWrap>(args.Holder());
 
   if (args.Length() < 1 || !args[0]->IsString()) {
     return env->ThrowTypeError("Bad arguments");
@@ -189,7 +189,7 @@ void FSEventWrap::Close(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args.GetIsolate());
   HandleScope scope(env->isolate());
 
-  FSEventWrap* wrap = Unwrap<FSEventWrap>(args.This());
+  FSEventWrap* wrap = Unwrap<FSEventWrap>(args.Holder());
 
   if (wrap == NULL || wrap->initialized_ == false)
     return;

src/handle_wrap.cc

@@ -47,7 +47,7 @@ void HandleWrap::Ref(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args.GetIsolate());
   HandleScope scope(env->isolate());
 
-  HandleWrap* wrap = Unwrap<HandleWrap>(args.This());
+  HandleWrap* wrap = Unwrap<HandleWrap>(args.Holder());
 
   if (wrap != NULL && wrap->handle__ != NULL) {
     uv_ref(wrap->handle__);
@@ -60,7 +60,7 @@ void HandleWrap::Unref(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args.GetIsolate());
   HandleScope scope(env->isolate());
 
-  HandleWrap* wrap = Unwrap<HandleWrap>(args.This());
+  HandleWrap* wrap = Unwrap<HandleWrap>(args.Holder());
 
   if (wrap != NULL && wrap->handle__ != NULL) {
     uv_unref(wrap->handle__);
@@ -73,7 +73,7 @@ void HandleWrap::Close(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args.GetIsolate());
   HandleScope scope(env->isolate());
 
-  HandleWrap* wrap = Unwrap<HandleWrap>(args.This());
+  HandleWrap* wrap = Unwrap<HandleWrap>(args.Holder());
 
   // guard against uninitialized handle or double close
   if (wrap == NULL || wrap->handle__ == NULL)

src/node.h

@@ -212,8 +212,9 @@ inline void NODE_SET_PROTOTYPE_METHOD(v8::Handle<v8::FunctionTemplate> recv,
                                       v8::FunctionCallback callback) {
   v8::Isolate* isolate = v8::Isolate::GetCurrent();
   v8::HandleScope handle_scope(isolate);
-  v8::Local<v8::FunctionTemplate> t = v8::FunctionTemplate::New(isolate,
-                                                                callback);
+  v8::Handle<v8::Signature> s = v8::Signature::New(isolate, recv);
+  v8::Local<v8::FunctionTemplate> t =
+      v8::FunctionTemplate::New(isolate, callback, v8::Handle<v8::Value>(), s);
   recv->PrototypeTemplate()->Set(v8::String::NewFromUtf8(isolate, name),
                                  t->GetFunction());
 }

src/node_contextify.cc

@@ -634,7 +634,7 @@ class ContextifyScript : public BaseObject {
     }
 
     ContextifyScript* wrapped_script =
-        Unwrap<ContextifyScript>(args.This());
+        Unwrap<ContextifyScript>(args.Holder());
     Local<Script> script = PersistentToLocal(env->isolate(),
                                              wrapped_script->script_);