Add v8 Function Converter ToV8 to gin

This changes adds the ToV8 converter to gin for v8::Function
This is used by electron internally and could be helpful to other
embedders as well.

Change-Id: I19067d1f5cb119a58f1a8574dd9f232b72b328bf
Reviewed-on: https://chromium-review.googlesource.com/c/1461826
Auto-Submit: Nitish Sakhawalkar <nsakhawalkar@slack-corp.com>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630782}

AUTHORS

@@ -1033,6 +1033,7 @@ Pengutronix e.K. <*@pengutronix.de>
 Rakuten Kobo Inc. <*@kobo.com>
 Rakuten Kobo Inc. <*@rakuten.com>
 Seznam.cz, a.s. <*@firma.seznam.cz>
+Slack Technologies Inc. <*@slack-corp.com>
 Spotify AB <*@spotify.com>
 Tableau Software <*@tableau.com>
 TeamSpeak Systems GmbH <*@teamspeak.com>

gin/converter.cc

@@ -151,6 +151,11 @@ bool Converter<std::string>::FromV8(Isolate* isolate,
   return true;
 }
 
+Local<Value> Converter<Local<Function>>::ToV8(Isolate* isolate,
+                                              Local<Function> val) {
+  return val.As<Value>();
+}
+
 bool Converter<Local<Function>>::FromV8(Isolate* isolate,
                                         Local<Value> val,
                                         Local<Function>* out) {

gin/converter.h

@@ -121,6 +121,8 @@ struct GIN_EXPORT Converter<std::string> {
 
 template<>
 struct GIN_EXPORT Converter<v8::Local<v8::Function> > {
+  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,
+                                   v8::Local<v8::Function> val);
   static bool FromV8(v8::Isolate* isolate,
                      v8::Local<v8::Value> val,
                      v8::Local<v8::Function>* out);